* o 0 0 V v * A SERIES OF POPULAR CHYMICAL ESSAYS: Containing a Variety of Inftances of the Application of Chymiftry to Arts and Manufactures; the Explanation of natural Phenomena; and to other ufeful Purpofes . MEMBER OF THE ROYAL MEDICAL SOCIETY OF EDINBURGH, AND LATELY PRESIDENT OF THE NATURAL HISTORY SOCIETY OP THAT CITYo THE SECOND EDITION. LON DO N: PRINTED FOR J. JOHNSON, IN ST. PAUL’S CHURCHYARD; By Bye and Law, St, John’s Square, Clerk en well. BY 1804 . TO THE GOVERNORS, and other SUBSCRIBERS, OF THE KETTERING DISPENSARY, TIIEIll READY AND LIBERAL ASSISTANCE t 'ft IN PROMOTING TIIE ESTABLISHMENT, ’ AND SUPPORTING THE CONTINUANCE, OF THAT USEFUL AND CHARITABLE INSTITUTION, THIS HUMBLE EFFORT OF THE AUTHOR, TO DIFFUSE USEFUL INFORMATION, IS GRATEFULLY DEDICATED \* BY THEIR HUMBLE SERVANT, Kettering, Oct. 7th, 1802. FENWICK SK RIMS HIRE. PREFACE. 1 he fubftance of the prefent effays is part of the materials, collected by the author with a view of delivering an ex- perimental courfe of popular lectures on Chymiftry and Natural Hiftory. Profef- fional engagements having prevented the adoption of his intended plan, it was thought by him, that it might prove acceptable to the public in the prefent form. It is not to be conlidered as a ftrictly fcientific work, but rather as one adapted to convey ufeful information to the clafs called general readers, by which is meant, thofe who are delirous of an acquaintance with various literary and fcientific fubjedts, without entering into the minutiae of any fcience. A 3 VI PREFACE. The fubje<5ls, here treated of, being elu- cidated and explained upon their true prin- ciples, the work is calculated to remove many erroneous conceptions concerning common occurrences. By pointing out very frequent applica- tions of chymical knowledge to ufefu! pur- pofes, the reader will be led to form a notion of the extenfive utility of the fci- ence,, and by preferving a connection be- tween; t lie fuhjeCts of the different effays, it is prefumed that he will have formed a general idea of the whole fyftem of Chy- miftry. Should the view, that is here given, ex- cite a fingle reader tc a further profecution of the ftudy, or fhould the fubjeCt, as here treated, be the means of diffufing informa- tion, that is at all ufefu], the author’s am- bition will be fully gratified. PREFACE. yn Subjects conne6led with Chymiftfy are fo numerous, that the work might eafily liave been fwelled to a much larger fize; but by attempting too much, we frequently effect nothing. It is hoped that the felec- tion will be thought judicious. The prefent work differs effentially from the fcientific and well-received “ Chymical Effays” of Dr. Watfon. He has given complete effays on fingle detached fub- jefits, whereas the author of the prefent work has introduced a very great variety of interefting matter into each effay, and has connected the different effays together into a feries. He has alfo been careful to fele£t fubjeels, that are more generally in- terefting. In a work of this kind the materials mult of courle be collected from a variety of authors, whom it would be ufelefs and tire- A 4 Viii PREFACE. fome to quote. Chaptal, Prieftley, Sauf- fure, Pictet, Fourcroy, St. Fond, Rumford, Kirwan, Bancroft, Saunders, and many others, have been occafionally had recouife to; and fome of the experiments related by Mr. Henry, in his valuable Epitome of Chymiftry, have been felefled as appropri- ate, and particularly correct. IX TABLE of CONTENTS. ESSAY I. PAGE OBJECT AND UTILITY OF CHYMISTRY i Object and utility of chymiftry illuftrated by thofe of geography • i And aftronomy • 2 Chymiftry defined * 3 Its object explained by experiment 3 Nature of chymical a&ion 3 Examples of chymical a&ion. 4 Analyfis ...... 6 Synthefts • 6 Chymical affinity 7 Its utility in the arts • • • • • • * 8 as in dyeing 8 bleaching ......... . — ........ . g tanning 8 . g, * pottery - ........... . 10 - metallurgy 1 1 - the manufacture of vinegar ...... 14 • in the fciences • as medicine j £ in natural philofophy r . id A S X CONTENTS. ESSAY II. PAGE CHYMICAL ELEMENTS. 17 Mistaken notion of the ancients 17 What we now confider as elements, may by future chymifts be afcertained to be compounds 18 Elements enumerated . . 18 Why taken as the bails of arrangement in the prefent work 19 ESSAY III. CONNEXION BETWEEN MEAT AND LIGHT ao The fun’s rays produce heat only when they meet with an opaque body. * 21 Different coloured fubilances abforb heat in different proportions 22 Thermometer more fenfibly affe&ed by heat when blackened 23 Heat refle&ed from the furface 6f water 23 Eifetts of black and white walls for fruit trees ..... 24 Heat without light . . 25 Light without heat 26 ESSAY IV. HEAT IN PARTICULAR. a 7 Expanjton ly heat 27 Moil bodies expand when heated, and contract when cold 27 Water an exception ; t , f# # t # t , , 27* CONTENTS. xi PACE Force of water In the a& of congelation 28 Advantages of the fame 28 Expanfion of metals by heat f ..... . 28 Glafs broken by fudden heat or cold . 30 Expanfion of fluids 31 Thermometer 31 Pyrometer 35 Expanfion of water, peculiarity of 36 Expanfion of air 39 ESSAY v. HEAT IN PARTICULAR. Effeftt of heat in converting folids into fluids , and fluids into vapour 4 \ Vaporization influenced by preffure 42 Digefters 45 Cold produced by melting folids, or vaporizing fluids 46 Freezing mixtures 47 Cooling of wine or water .".... 49 Capacity of bodies for heat so Conducing power 31 Ufe of double windows 52 ESSAY VI. HEAT IN PARTICULAR. Combuflion ....... 53 Combuflible body is not abfolutely defiroyed ..... 53 Nor is it the fource of heat and light 54 Air neceffary to combuflion 54 CONTENTS. PAGE Smoky chimnies 55 Argand’s lamp 59 Flame, nature of . 59 Economifmg of fuel 59 Lofs of heat in cooking 60 How obviated .... 63 Count Rumford’s roalfer 64 ESSAY VII. HEAT IN PARTICULAR. Different fources of heat 68 Friction .. 68 Concuhion , 69 Changes in the chymical compofition of bodies .... 69 Py rophori 70 Senfation of heat 71 ESSAY VIII. LIGHT IN PARTICULAR • 73 Chymical effeds of light 73 • — upon nitric acid 73 — * vegetable powders 74 different dyes • • • • 74 ■ vegetation ••••• • 76* Subftances that become luminous by the ahforption and remiflion of light 79 Light by attrition 80 ELedric light • • • • •••••• •*•••* .. .. ...... , , , . 8 t CONTENTS. ESSAY IX. PACE THE GASSES. Gas differs from vapour 82 Oxygen gas * • . 84 how procured • • 84 • its properties • • • •••» 84 Muriatic acid - 85 — its ufe in bleaching • • • • • 86 Common fait • ••• 86 Atmofpheric air • •*. 88 — — neceffary to the life of animals* • 89 Ventilation . ••• 90 Air vitiated by combuftion 93 Dews, fogs, rain, & c. * • • • ........... 94 ESSAY x. AZOTIC GAS 99 Its properties 99 Putrefa&ion 100 Aqua fortis 10 1 its effe&s on flefti 102 Saltpetre * ••• 103 Gunpowder, composition of 104 Fulminating powder* * * * 106 Nitrous gas 106 Eudiometer. . 7 - . . . 107 Nitrous oxyde 107 — — peculiar effefts of, when breathed . , 108 9 XIV CONTENTS ESSAY XI. PAGE- HYDROGEN GAS 109 How procured 109 Iis properties no Artificial fireworks no Aurora borealis in Fire-damp • • • • * n r Air balloons • • 1 1 3 Water, formation of • • • • • . 114 Effects of the decompofition of water coming into contaft with melted metals 116 Prefervation of water ........ 116 ESSAY XII. CARBON, OR CHARCOAL 118 CARBONIC ACID GAS, OR FIXED AIR 12 1 PuPvE carbon 1 1 S Common charcoal • • 1 1 8 Diamond, combuflible 119 Carbonic acid gas, how procured 120 Fermentation of wines 121 Fixed air, the caufe of their brilknefs 123 Difference between old and new wine I23 To make beer 123 Fixed air from combuftion of charcoal 127 JBad effects of it when breathed 127 Treatment of perfons fuffocated by it 128 Fixed air from refpiration 128 Choak damp 129 To prevent bad effofts of fixed air 130 CONTENTS. xv PAGE Seltzer water '. * 131 Petrifa&ions 132 Fixed air from burning of lime 132 ESSAY XIII. CARBON, COALS AND OILS 134 COMPOSITION of coals 134 Coalmines 13 $ Varieties of coals 137 Coke , 139 Origin of coals 140 Oils . . 141 Caufe of tkeir rancidity . 141 Drying oils 142 ESSAY XIV. PHOSPHORUS 143 Properties of Phofphorus 143 Very eafily inflamed* •• 144 Luminous oils • 144 Gas -• • • • 143 Phofphoric match bottles • • 145 Phofphoric acid * 146 Phofphorus obtained from bones 146 f rom U rine 147 Natural phofphori • • • • 147 Glow worms 1 48 Phofphoric light from putrid animal and vegetable matter • • 149 xvi CONTENTS. ?ACK DiiTertation on the luminous appearance of the fea 1 5 1 V ariety of its appearances 152 Caufes of the appearance 154 Fir ft, putrid fifh •»••••••• 155 Second, living infers and fifti fpawn 158 Ignis fatuus 160 — origin of many fuperftitious tales • • • • 161 Arguments againft fuch tales , , . . 162 ESSAY XV. SULPHUR, OR BRIMSTONE 164 Where found, and how prepared 164 Sulphuric acid, manufacture of 165 Sulphurated hydrogen gas 165 Harrowgate water . 166 ESSAY XYI. THE ALKALIES 167 Qualities of the alkalies 167 Ammonia « • • 167 Sal ammoniac . . • • * 168 Fixed alkalies •*•••• 169 Soap making * 1 7 1 Glafs making • 173 ESSAY XVII. THE EARTHS 176 Their names 176 Xime * ...... 176 CONTENTS. Chalk : limeftone Mortar of the ancients, why harder • . . Marl Marble * Their fuppofed origin Spar Gypfum Hard waters, caufe of Magnefia Clay Ericks and tiles # Stone ware Porcelain Glazing of earthen-ware Alum, manufacture of Flint and other filiceous ftones ESSAY XVIII, xvii PAGE i n *79 179 1 8 x 181 182 183 184 186 187 187 188 188 189 190 1 9 1 EARTHS. 5UILS AND MANURES Properties of a good foil ....... ....... , 93 Different kinds of foil 9 , Paring and burning Different kinds of manure Rules for felefting the proper manure » . . , , ESSAY XIX. , 97 ■ the metals.....,,.,, in which they are found . . . . Gold, how and where found xviii CONTENTS. IPAtVR Art of gilding • 204 Silver • •• 205 Silvering and filver plating 205 Mercury has been frozen • 206 To filver looking -glaffes • 206 Cinnabar and vermilion • • • • * 207 Copper and brafs 207 Tinning of copper 208 Verdigrife 208 To brown fowling-pieces 209 Iron • • • • 209 Steel 209 Black-lead ••••••••• 210 Ink, compofition of 210 To take out ink fpots 210 • iron moulds, &c 2 1 1 Tin plates, how made * • • • • • 212 Lead 212 White lead. Shot 213 How to deteft lead in wines or other liquors • • • • 214 Tin 215 Tinning of pins 215 Drofs of tin and lead revived 216 Zinc, calamine, and black jack «■ 216 Galvanifm, the laws of 217 Galvanic pile ? 219 Cobalt 220 Arfenic 221 Baneful effefts of arfenic .•*•»••••••..••••••• 221 1 CONTENTS. xix - it ESSAY XX. PAGE MINERAL WATERS 224 Simple waters, cold , as Malvern 225 - warm, as Briftol, Buxton, and Matlock 226 Chalybeate waters, hot, carbonated, as Bath, Vichy, and Carllbad • • • • 228 Cold, carbonated, as Tunbridge, Spa, anVl Pyrmont, Cheltenham, and Scarborough • • • 231 Variolated, as Hartfell 233 Saline waters. Simple, as Epfom and fea water 234 ■ highly carbonated alkaline, as Seltzer 236 Sulphureous waters, as Harrowgate •••••• 237 Table of mineral waters •••••••• 239 ESSAY XXI. ARTIFICIAL MINERAL WATERS 245 To imitate the iimple waters » 246 chalybeate waters 247 faline waters 249 — fulphureous waters 250 ESSAY XXII. ON THE RED WELL AT WELLINGBOROUGH .. 253 Much celebrated in former times .. 233 Situation of the well 254 Appearance and properties of the water ... 253 Similar to that of Tunbridge 255 In what difeafes ufeful 25S Rules for drinking it 257 XX CONTENTS. ESSAY XXIII. ON DYEING .. P *259 Of fubftances to be dyed 259 Of mordants ...... . 261 Of colouring drugs 264 Red dyes . ... 264 Yellow dyes 267 Blues 268 Compound colours, as fcarlet 269 * green 271 — violets, purples, and lilacs . 271 — —black 272 — — g™y 2 73 ESSAY XXIV. OF TANNING 274 Preparation of the Ikins 274 Tanning ............... 275 Handling 277 Of different tans 278 Different improvements ... 279 Defmond’s plan 280 ESSAY XXV, OF CURRYING 286 Shaving . *. 287 Scouring 287 Stuffing • * • 9 • * • • * 4 •••.'.< . . . c • 288 Rolling . 2^9 Blacking • . aoo ESSAY I. TIIE OBJECT AND UTILITY OF CHYMISTRY. To the {Indent, defirous of information, two que (lions naturally arife on hearing the name of any fcience, profeflion, or art, which has not been the fubject of his {Indies. He firft inquires what is the object of this science, profeffion, or art, and what kind of information it affords. He then as eagerly demands to be informed of its utility * Suppofe geography to be the fcience; what is geography ? he afles ; what does it teach ? or what does a knowledge of it imply? Geography, he is told, is the fcience, that teaches us the divifion of the globe into land and water ; the former into kingdoms, and fmaller portions; the latter into feas. lakes, and rivers; and then teaches us the relative fituation of thefe various parts. What is the advantage of this knowledge? is the next queftion ; and he is told in anfwer, how much the traveller is benefited by it in traverfing diflant regions ; how ufeful it is to the general marching into an enemy’s country; how neceffary to the fludent of natural hiftory ; and how requifite to the philosopher, itudying the manners, moral and poli- tical, of different nations. B £ THE OEJECT AND UTILITY If aftronomy is the fubjeft of inquiry, the fame questions arife; and he is informed that its obj eft is, to teach the fituation and motion of the fun, planets, and other heavenly bodies ; their fitua- tion with refpeft to the earth, and to each other ; and their motion in their refpeftive orbits, as well as on their own axes. As to the advantage of fuch knowledge, it is various, and important. It enables us to foretel the change of feafons, as well in countries that we never vifited, as in our own ; to explain and to predict various natural phenomena, as eclipfes, conjun&ions of the plan- ets, and the appearances of comets; and by the aid of calculation it teaches the navigator to fleer his courfe through unknown feas, and to afcer- tain his precife fituation either on the ocean, or on the land, though in climes never before vifited by man. Similar queftions to the above mud naturally arife refpe&ing other fciences; and the anticipa- tion of them refpefting chymiftry will furnifh us with matter for the prefent effay ; forming an appropriate, and, I trufl, interefting introduftion to the reft. In pointing out the objeft and utility of chy- mijiry , I fhall explain in a general way the advan- tages that have been derived from it, in its extenfive application to the arts; and the affift- ance it affords us in explaining a variety of OF CHYMISTRY. S natural phenomena, and in ftudying the other fciences. Chymistry, to define it, or exprefs its obje£t in a few words, may be faid to teach us, the changes that are effected in the component parts of bodies by their mutual aftion. But as definitions are always dry, and the beft may become the fubjefl: of cavil and difpute, I (hall endeavour to illuftrate and explain my meaning by the relation of a few fimple experiments. When a piece of marble or a piece of chalk is dropped into a glafs of aqua fortis or a glafs of vinegar, an effervefcerice immediately takes place, or the liquor froths, in confequence of the extri- cation of air or gas; the marble or chalk is gradually dififolved, and the liquor at length remains clear and tranfparent. Certain changes have here been effected in the component parts of the marble and the acid, by their mutual action of the one upon the other; and it is the objedl of chymiftry to teach, both what thefe changes are, and how they have been effe&ed. What is called practical chymiftry teaches us the firft, and theoretical chymiftry the fecond part. This aftion of the acid upon the marble, and of the marble upon the acid, differs materially from any kind of mechanical aftion, and is called a chymical action. For inftance, it differs mate- rially from the mere diffufion that takes place B * 4* THE OBJECT AND UTILITY when fand and water, or oil and water, are agitated together in a phial. By fhaking they are made to act mechanically , and for a moment the fand or the oil is diffufed through the water; but no fooner do you ceafe to agitate them, than they inftantly feparate; the fand fubfides to the bottom, or the -oil fwims on ;the furface of the water. But with refpeft to the marble and the acid, the former is-not merely diffufed; they have afted chymically, and the marble will not be depofited on ftanding, nor can they be again feparated but by other chymical .aftions. The peculiarity of this kind of aftion, in which it differs from other kinds, is, that it only takes place at immeafurable and infenfible dif- tances ; it being neceffary to chymical action, that the particles of one body fliould be in clofe con- tact with thofe of the other. Hence it follows, that few folids can be made to aft chymically on each other, a fluid and solid more eafily, and two fluids Hill more fo, becaufe their particles are more readily brought into contact. Inflances however may be brought of chymical aftion between fubftances in all thefe forms ; and we fhail feleft for examples fuch as will prove very amuling and interefting experiments. As an inftance ot two folids being brought to aft -chymically, rub together in a mortar fmall por- tions of brimltone and the oxymuriate of potafh. OF CHYMLSTRY. 5 By trituration* they are made to act on each other, and the confequence is repeated flafhes, and flight explofions. A finall portable apparatus for per- forming this experiment may be had at the (hops in London.. As an inftance of a folid and a fluid, drop fome potalh into an infufion of rofes; and as an exam- ple of two fluids, pour an acid into the fame infu- fion : by the former the red liquor will become green, and by the latter addition it will recover its original colour, or rather become bright red: this change may be repeated on the fame liquor as often as you pleafe by the alternate addition of an alkali and an acid. As another example of two fluids afting chymi- cally on each other, mix together a faturated folu- tion of Epfom fait in water, and a faturated folution of muriate oi lime. In this experiment the two tranfparent fluids are fuddenly corr verted into one folid mafs, and that without freezing. Laftly, as an mflance of chymical aftion between two galles or aeritorm fluids, mix the common air of the atmofphere with nitrous gas, as in the common eudiometer, and a diminution of volume, and for- mation of nitrous acid, inftantly take place. The above experiments are all examples of chy- mical actions ; and it is the objefl of chymiftry to afcertain, and to explain, the various changes that have taken place in them. 6 THE OBJECT AND UTILITY When two fimple bodies are made to unite chy- mically, we call the fubftance refulting from the union a compound. This compound may again unite either to a fimple or to another compound, forming in the firft cafe a triple fubftance, or in the laft a compound of four fimples ; and thefe again may unite to others, forming fubftances ftill more compound. Now it is one of the grand objefts of chymiftry, to feparate thefe compounds into the fimple ele- ments, ot which they are compofed ; and the operation by which it is performed, is called ana - lyfis. When we have accurately analyfed any com- pound fubftance, we may often reproduce it by properly combining the fimple fubftances, of which we have difcovered it to be compofed. This pro- cefs is termed fynlhejis , which in the inveftigation of any chymical fubftance forms with the former, namely analyfis, the complete chymical teft. Of what I have here faid I fhall now give an example in the decompofition and recompofition of Epfom fait. By diffolving it in water, and then adding an alkali, the foffil alkali, called foda, for example, an earthy powder is precipitated, which, when colle&ed by filtering the diquor through paper, is found by particular chymical tefts to be magnefia. The filtered liquor by fur- ther tefts is difcovered to be nothing but Glauber’s OF CHYM1STRY. * fait diffolved in water. Now Glauber’s fait is known to be foda combined with fulphuric acid, or oil of vitriol, the former of which was added in the experiment. We have here analyfed Epfom fait, and found its conflituent parts to be magnefia and fulphuric acid. If magnefia be diiTolved in fulphuric acid, di- luted with water, and the liquor evaporated, a fait is cryftallifed, that is tound to be Epfom fait ; fo that we have here the fynthetical proof, that Epfom fait is a combination of magnefia and ful- phuric acid; Some chymical fubllances have a greater difpo- fition to unite than others, as fulphuric acid and foda, than fulphuric acid and magnefia, in the above experiment. This is termed their chymical attraction, or affinity ; and in chymical language we fay, that fulphuric acid and foda have a flronger affinity, than the former and magnefia ; or we fay that fulphuric acid has a flronger attraction for ioda than for magnefia. It is in confequence of thefe different affinities, that we are enabled to decompofe one fubftance by the addition of another, as Epfom fait by the ad- dition of foda ; and it is the objeft of chymiftry to teach the degrees of thefe affinities between different fubllances, whereby the chymift is able to foretel the confequence of mixing fuch and fuch fubllances B 4 8 THE OBJECT AND UTILIT* together; and he who knows the mod in theft refpefls is the belt pra&ical chymifl. I have now explained ~ the- objeft of chymiftry, and fhall therefore proceed to point out fome of the moll linking inllances of its utility, and its ap- plicability to ufeful purpofes. Almoll every art may be confidered as a chymical procels ; and although we fee many of them daily performed by the moll ignorant people, and al- though fome may have been originally difcovered, and even brought to their prelent flate, without any affillance from the chymifl, yet they become to him interefting objefts of attention ; and it is only by his aid, that the nature of the procefs can be underllood, and explained. It is by fuch know'- ledge that very many have been Amplified, and im- proved ; nor are the original difcoveries of the chymifl: few or unimportant. In the art of dyeing , every part of the procefs is chymical, and many improvements have been made in it by fcientific men. Dr. Bancroft in this country, and Berthollet in France, have within thefe few years done much in Amplifying the opera- tions, and in rendering them lefs expenfive. They have alfo improved the dyes in fome cafes, and in- troduced many new colouriug drugs, the particulars of which will fall more properly to be noticed in an elfay on this fubjeft. OF CH Y MTS TRY. 9 Bleaching again, which ten years ago was a pro- cefs of many months, may now be lefs expenfively and more completely performed in as many days. The difcovery of oxygenated muriatic acid, by which this great improvement in the art of bleach- ing has been effected, was made by Scheele, a Swedifh chymift; and Berthollet, a Frenchman, has the honour of having firft applied it to this purpofe ; and various fcientific men in this country have improved the mode of ufing it. Every ma- nufacturer has now taken advantage of this dif- covery, by which the extenfive bleach-fields are contracted, and their goods brought to a much earlier market. Tanning is another art, that has been very much, and is likely to be ftill more improved, by having become the fubjeCt ol chymical invefligation. In tanning, the objeCt is, to convert the foft and porous hide into a more hard and compaCl fub- fiance, that is lefs eafily penetrated by water, and lefs liable to putrefaction. This has always been chiefly effeCted by long continued immerfion in an infufion of fome bark, moft commonly oak bark, Seguin, a Frenchman, examining the nature of the procefs fcientifically, and afcertaining the chymical qualities of the intufion, found that it is not, as generally believed, the aftringent quality of the bark, that operates the change, but a diflinCt prin- ciple, now called the tanning principle, which ex- B 5 10 THE OBJECT AND UTILITY ills in different proportions in the hark of different trees. This tanning principle he has devifed the means of extra&ing, and applying to the hides in a more concentrated form, than it had hitherto been ufed ; by which means hides, that required twelve or eighteen months, may now be tanned in lefs than as many weeks, and of courfe be brought to market at a much lower price. In the making of pottery and porcelain every one mull be aware of the great improvements that have been introduced within the lalt ten or twelve years ; and it is generally known too, that to Mr. Wedgwood we are indebted for moll of thefe valuable improvements. This fcientific ma- nufacturer accurately analyfed the bell foreign wares, to difcover of what earths they were formed, and in what proportions ; he examined in the fame way different antique vafes, and other articles, and by a very ingenious contrivance, which will be noticed in a future effay, he invented the means of afccrtaining the exa£l degree of heat, to which any fuch articles had been expofed in their baking. He then fought through various parts of this country for earths, fuch as he wanted ; what he could not find, he formed artificially by the due admixture of others; and, by all thefe means combined, he has been enabled to imitate the wares of China, and of other countries, that excelled us ; and has invented different kinds, both 4 OF CHYMISTRY. 11 more ornamental and more ufeful, than what were before manufa&ured. It will require little confideration to (how the application of chymiftry to metallurgy . None of the metals are found naturally pure and un- combined, at lead not in any confiderable quan- tity. They are united fometimes with fulphur, fometimes with pure air under the form of calces, fometimes with acids, and often with each other. Copper, for inftance, is found in all thefe dates ; in the' form of pyrites with fulphur, of calx with pure air, of blue vitriol with fulphuric acid, and often mixed with filver, and other metals. It is true that the means of feparating and purifying many of them have been accidentally difeovered by unfcientific men ; but with how much more certainty, and how much more Amply, will he execute the bufmefs, who, acquainted with the affinities, and other laws of the fubltances he em- ploys, knows exaftlv, what will feparate their.com- ponent parts, and what will purify them from ad- ventitious matter. One or two inflan ces of the advantage of chymical knowledge in this depart- ment will fufficiently evince the extenfive appli- cability of it to metallurgy. Copper is frequently found combined with vi- triolic or fulphuric acid in the form of blue vitriol ; and in the mines, where it is found in tins date, there are frequently dreams of water very much B 6 12 THE OBJECT AND UTILITY impregnated with this copper ore, which were formerly thought ufelefs, and were confequently negleCted. Chymiftry teaches us that fulphuric acid has a Wronger attra&ion for iron than for copper; of which fact you may eafily convince yourfelf by the following fimple experiment: DifTolve fome blue vitriol in water, and immerfe into this folution the blade of a knife, a key, or any other piece of po- lished iron, and you will prefently perceive its furface to be covered with a layer of copper, the acid of the vitriol having feized on the iron, and in the fame proportion depofited the copper. To apply this ufefully to the point in queftion, it is only neceffary to throw old ufelefs iron into thefe {breams, and a depofition of good copper will be gradually effected ; which is a plan, that is now very generally praftifed. As another inftance, fomewhat fimilaf to the former, of advantage derived from chymiftry, I fhall mention a mode of obtaining green “vitriol adopted in a manufactory at Newcaftle. There is often found among the coals of that place a large quantity of an ore, called pyrites, which, as it injures the quality of the coals, is always separated from them, and was heretofore confidered as ufe- lefs. The chymift has now taught the manufacturer to convert thefe pyrites into green vitriol, and has OF CHYMISTRY. IS thus rendered valuable what was before eonfidered as ufelefs. The pyrites contain both iron and fulphur;. green vitriol is a combination of iron and fulphuric acid ; what is to be effected therefore is, to convert the fulphur into fulphuric acid, and difpofe it to unite with the iron. This converfion only requires, that the fulphur fhould be made to combine with oxygen, or the pure part of the air, for fulphuric acid is fulphur acidified by oxygen, and the mode adopted in the prefent in fiance is as follows. A large area of ground is enclofed, that has a gentle declivity; the furface is made even, and is covered with a fat clay, and a furrow is formed in the midft of it, to collect and convey the water to proper refervoirs. The pyrites are fpread out in layers on this area to the height of feme feet, and by expofure to the air, rains, and other vicifTitudes of the weather, they foon heat, fwell, and fall into powder. This operation is affifled by turning the pyrites with rakes, that have iron teeth, and by occafionally fprinkling them with water, when the feafon is dry. The fulphur by this procefs abferbs the oxygen or pure part of the air, which converts it into fulphuric acid. This acid feizes the iron, and forms green vitriol, which, duTolved in the water, is conveyed into the refervoirs. From thefe reiervoirs it is carried to coppers, where it is boiled, and evaporated to a fufficient llrength. It is then THE OBJECT AND UTIL1TT » ‘ cryflallifed by cooling in wooden troughs. This green vitriol, martial vitriol, or copperas, as it is often called, forms an article of traffic, and is ufed by dyers, and frequently by curriers, as alfo in many other of the arts ; and it is a principal ingre- dient in the making of ink. It is likewife a very fervic cable medicine in a variety of complaints. In brewing , baking , making wine , J pints , vine- gar, &c., we have pure chymical procefles, that can only be thoroughly underflood by the chymifl, and are confequently moft likely to be improved by him. To enumerate and defcribe all the im- provements made by chymifls in thefe and other arts, would be improper in an introduftory efTay. I fhall therefore now* conclude the applicability of chymiftry to operations of art, by a late improve- ment in the art of making vinegar in the large way. It is a faft now well known, that beer, wine, fugar and water, and other fuch liquors, become four, in confequence of their abforbing or im- bibing the pure part of the air, dr oxygen. It is alfo known, that the greater the furface of the liquor, that is expofed to the air, the more quickly it abforbs the pure part of it, and becomes four. This therefore is the grand point that is to be aimed at in the whole procefs ; and by conflantly pumping the liquor into a large cooler, through which it is allowed to run in a flow flream, and return to the vat, from which it was pumped, the OF CHYMISTRY. 15 furface thus expofed to the air is confiderably greater than it would otherwife be, and the time of making the vinegar is thereby very confider- ably Shortened. For the fame reafon, when it is made in the fmall way, the air fhould be freely ad- mitted, and the cafk be not more than half filled, that a greater furface may be in contaft with the air. The fubferviency of chymiftry to the other fei- ences might be expatiated upon very largely, but not without entering too minutely into the fciences themfelves. Medicine has been benefited by it in a variety of ways, in the compofition of remedies, as well as in the praftice. Almoft all the animal funflions, as refpiration, digeftion, &c. are chy- mical proceffes, fome perhaps peculiarly modified by the principle of life. Our breathing is a chy- % mical procefs, that until lately was hardly at all comprehended. The difeafes of the cheft, where the organ of refpiration is feated, will naturally be fuppofed to be connefled in a great meafure with the ftate of that funfiion. This is certainly the cafe ; and the phyfician therefore, who is ignorant of the nature of this chymical procefs, will be much lefs likely to employ the proper remedies, than one, who is well acquainted with this important func- tion. Numberlefs fuch inflances might be pointed out, to fhow the fuperiority of that part of the pro- feflion, that is well verfed in chymiftry, over fuch a know nothing of this fcience. 16 THE OBJECT AND UTILITY, &C. The natural philofopber , without the aid of chy- miftry, would form but an inadequate notion of the properties of air,, water, fire, or light. He would know that the air of the atmofphere is elaftic, pon* derous, and more or lefs compreffible ; but he would be ignorant that it is a compound of a pure and an impure air, the firft fupporting combuftion, and life by refpiration, whilft the other is unfit for either. The mineralog'ijl requires chymical tefis to dif- criminate between fubftances that to the eye appear fimilar, and to afcertain more fixed characters for diftinguifhing between one mineral and another. Laftly, the agricultural: may derive advantage from chymiftry by fcientifically examining the na- ture of the foil, and the nature of his manures, and by thefe means learning properly to adapt the latter to the former. I have now pointed out fome very palpable ex- amples of the ufeful application of chymical know- ledge. To explain more fully the proceffes, that I have here only hinted at, will occupy fome of the future Effays, in which I {hail likewife feleft fuch others, as are likely to prove rnoft interefting and moll ufeful. I fhall at the fame time endeavour to preferve fuch a connexion between the fubjefts of the different Effays, as fhall convey a general idea, at lead of the outlines, of the whole fcience of chymiftry. IT ESSAY II. CIIYAJICAL ELEMENTS. In every age there have been certain fubftances confidered by the philofophers of the day as ele- ments, or Ample fub fiances, of which every thing elfe has been fuppofed to be compounded. But what have been enumerated by the philofophers of one age as elements, have been afterwards 'proved by thofe of another to be compounds; and as the fciencc of chymiftry has been im- proved, we have difcovered the means of analyfing. or decompofing what was previoufly conceived to be a Ample. Thus water, from time imme- morial to a very late period, was allowed by all philofophers to be one of the elements of nature; modern chy mills have however decomposed it, and detefted with accuracy the ingredients of which it is formed, and even the proportions in which they exift. For many ages paft, and even to this day by many, earth, air, fire, and water* have been, and are confidered the four elements, of which this globe, and every thing terreftriai, are formed. Chymiftry now teaches us, that there are many kinds of earth, and many kinds of air, perfectly diltinft from each other, fame of which / IB CHYMICAL ELEMENTS. are compound, and feme fimple. It teaches us that fire, called now caloric, is a fimple fubftance ; and that water, as I laid before, is a compound. Although we can now treat more accurately of the elementary fubftances, we cannot fpeak de- cidedly; and you muft ftill keep in mind, that what are at prefent termed elements, may by future chy- mifts be difeovered to be compounds; and that we only mean, by calling them fo, to afTert that, in the prefent ftate of cliymical knowledge, they are not decompofafole. The fubflances at prefent confidered as elements are the followiilg. Caloric (the matter of heat or fire) ; light ; oxygen (the bafe of pure or vital air); azote (the bafe of impure air) ; hydrogen (the bafe of inflammable air); carbone, or pure charcoal; phofphorus; fulphur ; two of the alkaline falts, viz. foda and potafh ; the nine earths ; and all the metals. As thefe are the fimple fubftances at prefent known; a complete body of chymiftry would be given, by treating of their various combinations with each other ; and perhaps the moft fcientific fyftem would be formed by treating of each fim- ple fubftance feparatjely, and noticing under the head of each all jthofe compounds, that derive their meft remarkable properties from that particular ele- ment. Whether, however, this might or might not be the bell mode of forming a complete fyflem of CHYMICAL ELEMENTS. 19 chymiftry, it will afford a very convenient arrange- ment for the partial account intended to be given ii* the following Effays. It will afford us every op- portunity, that can be wiihed for, of noticing fuch peculiarities in the properties both of the elements and their compounds, as will be thought worthy of attention; and will lead us to notice their ufes, to explain any art to which they may be applicable, any feience to ’which they may be fubfervient, or any phenomena which they may tend to elucidate. The fame plan will aifo have the advantage of connefiing one Effay with another, and forming of the whole a conne&ed feries, that will be calculated to give a general idea of cbymiflry as a fcience. The order, in which the elements have been enumerated above, is the order, in which they will be treated of; firft then of heat and tight. so ESSAY III. TIIE CONNEXION OF HEAT AND LIGHT. There is fo intimate a connexion between heat and light, that we have in many inRances the ap- pearance of the one being converted into the other; they are frequently concomitants in the fame phe- nomena; and the fame caufes in a variety of in- fiances produce both. This their intimate connexion has given birth to a variety of hypothefes; and various conjec- tures have been hazarded in confequence, refpeft- ing the nature both of heat and light.' We mult 3 not however, in treating this fubjeft, indulge in thofe fpeculative opinions, that have occupied in vain fo much of the time and attention of philo- fophers, and concerning which there is ftill as much difcordancy as ever,, W e muft pafs over the long contended ques- tions, whether heat is a mere vibration of particles, or a particular fubftance; whether it is a modi- fication or a component part of light; or whether light* as feme fuppofe, is a component part of heat. In a popular work of this kind it would be highly improper to enter into abftrufe difquifi- tions on firch points, and w T e fhall therefore, in. CONNEXION OF HEAT AND LIGHT. 51 concurrence with- the generality of modern chy- mifts, fpeak of heat and light as fubftances, and .as diftinft and fnnple fubftances ; and we muft content ourfelves with noticing fome few inftances of their connexion, without attempting to explain them. The fun is generally confidered to be the common fource, and the only fource, both of heat and light ; and it is probable, that all proceeded originally from that fountain, although the light and heat afforded by combuftion, the emiftion of light from phofphorus, and of heat by friction, appear at firfl fight to be fo many inftances of diftinft fources. The rays of the fun feem to afford heat only when they meet with an opaque fubftance, and not when they pafs through a tranfparent one, as air, or water, or when they are reflefted by a white or polifhed one. The air is not heated im- mediately by the rays of the fun paffing through it ; but on their meeting with an opaque body, as the earth for inftance, heat is elicited, and is thence gradually communicated to the furround- ing atmofphere. This accounts for the intenfe cold of lofty mountains. If the rays of the fun warmed immediately the air, through which it paffed, the air ought to have the fame temperature in thofe regions, as in the vallies below ; but it is not until the rays are obftrufted by the earth, that they have the effeft of communicating heat; and 22 CONNEXION OF HEAT AND LIGHT. therefore the further we remove from the earth’s furface the greater is the degree of cold. When the fun’s rays fall upon a white or polifhed body, they communicate no heat ; and in propor- tion as fubftances have the power of reflefting the rays, is their temperature more or lefs increafed. An old but curious and interefting experiment may be brought in elucidation of this faft. If pieces of cloth of different colours (white, fcarlet, and black, for inffance) are laid at the fame time on the furface of the fnow, where the fun’s rays can fall upon them, they will be found after fome hours to have funk into the fnow to va- rious depths, according to their reflefting powers; the white, which reflefts the mofl light, will have funk the leaft ; the fcarlet, reflefting lefs, will have funk more; and the black, which reflefts little or none, will have funk by far the deepefl into the fnow. In this experiment the rays falling on the black being abforbed, and not reflefted, produce heat, which caufing the fnow to melt, neceffarily makes that piece of cloth to fink ; the others reflefting more of the rays, lefs heat is emitted, and confe- quently they fink lefs into the fnow. It is for the fame reafon that black clothes of all kinds arc much warmer in fummer than light-coloured ones. And the fame faft, we are informed by'Sauffeur, s known to the Swifs peafants, and taken advan* CONNEXION OF HEAT AND LIGHT. 23 tage of by them when the fnow lies too long upon the ground. He tells us, that, when this is the cafe, and they want particularly to fow their feeds, they arc in the habit of fpreading black cloths upon the furface of the fnow, to facilitate its melting. You will now eafily underftand, why a thermo- meter, that has its bulb blackened, is more fenfible to an increafe of heat than a common one; and why, when both are expofed to the light, the black- ened one indicates a higher temperature. In this cafe the rays of light, that are refle&ed by the com- mon thermometer, are abforbed, and emit heat in the blackened one, and confequently increafe the temperature of the contained mercury. • That it is the abforption of light in this cafe, that caufes the heat, is proved by interpofing a plate of tranfparent glafs between a thermometer and a lighted candle. The glafs will evidently intercept the rays of heat, and tranfmit only thofe of light, and yet the mercury in the thermometer will rife, and particularly if the bulb of it is blackened. The lultry heat experienced on the furface of the water in a funny day arifes from the reflec- tion of the rays of light. The temperature of the water is but little raifed, becaufe the light is re- flefted, and not abforbed: but the reflefted rays ? as well as the dire£l rays of the fun finking upon 24* CONNEXION OF HEAT AND LIGHT. any objefi, that is on the furface of the water, makes it fo much the hotter to perfons in that fituation. Some perfons reafoning upon thefe fa&s, that light when abforbed emits heat, and that black bodies abforb whilft white ones refleft it, have argued for the propriety of forming black walls for fruit trees ; but their reafonings are infufficient without experiments to determine the point, as will appear from the following confideration. The walls themfelves will no doubt be warmer than if they were white ; but the heat will be communi- cated from the walls to the air immediately in con- ta£f, and not to the fruit, which very feldom touches the wall, and then only by a fmall furface ; the heated air being unconfined, will mod of it pafs away, and thus the heat emitted by the abforption of light be of little advantage towards the ripening of the fruit. But if the walls are white, they re- lief!; the light ; and thefe reflected rays meeting with the opaque fubftance of the fruit, and other part of the trees, emit heat, that is direfily applied to the defired purpofe. The fruit is in this j-efpe£T precifely in the fame fituation with a perfon on the furface of the water. It is therefore neceffary to determine by expe- riments, to what extent the temperature of the air is increafed at the diftance from the black wall, that the fruit ufually hangs ; and whether it is more 6 Connexion of heat and light. £# more than equivalent to the heat emitted by the ab- forption of rays refle&ed from the white wall. In a pinery, however, or other hot-houfe, par- ticularly where there is no fruit growing near the wall, I conceive that a black wall would be d6-- cidedly preferable to a white one; for here the air, heated by the warmth of the wall, not being allow- ed to efcape 5 would increafe the temperature of the whole air in the houfe; whereas the rays refle&ed by a white wall would many of them pafs again through the glafs of the windows and the roof* without adding to the warmth within. Befides the above inftances of intimate con- nexion between heat and light, the phenomena of combuftion afford ftill others. When the tempera, ture of a piece of iron is raifed to the flate called incandefcence, that is until it becomes red hot, it emits light as well as heat; and when a more inflammable fubflance is heated, combuflion is the confequence, during which there is a rapid extri- cation of light in the form of flame. The fource of the light in thefe inftances is ftill a matter oj difpute. Although heat and light are in fo many inffan- ces very intimately connefted, we have examples of the exigence of the one without the other. By friftion, heat is extricated unaccompanied by light. Itt c £6 CONNEXION OF HEAT AND LIGHT. In phofphorus, and other bodies pofleffing phof- phorefcent qualities, as glow worms, fhining fifh, and putrid animal and vegetable fubflances, we have light without heat ; at leaft the means have not yet been difcovered of rendering the heat fenfible. And again, the rays of light refle6Ied from the moon have not yet been fatisfaftorily proved to emit heat. 1 7 ** ESSAY IV. HEAT IN PARTICULAR. EXPANSION BY HEAT. 'Our obfervations on heat in particular will be J^eft arranged by confidering feparately the general effefts of heat. Thefe are, lft. Expanfion; 2dly. A change of form, as from folid to fluid, or from fluid to vapour; and Sdly. Combuflion. Expanfion by heat . All bodies, whether in the folid, fluid, or gaseous ftate, are more or lefs ex- panded in every dire&ion by the application of heat; unlefs in fome instances, where there feems to be a chymical change in the nature of the fubftance, as in the baking of clay, where there is a contraftion in all dimenfions, inftead of expanfion, which feems to arife from a femifufion, during which there is an alteration in the arrangement of the particles, ap- proaching fomewhat in its nature to the cryftal- lization of falts. As bodies in general expand when heated, fo -do they contraft when cooled ; but to this there is an exception in the freezing of fluids, where, in confequence of the new arrangement in their par- ticles, there is always a confiderable expanfion, The force with which water expands when in the a£t of congelation is immenfe. Mufcheru C ft £8 HEAT IN PARTICULAR. broeck, who made experiments on this fubjefl; by freezing water in metallic globes, found the force fufficient to burft one of brafs, that would have required a force equal to 27700 lbs. to have burft it. It is by this means that huge fragments of rocks are feparated; the water that penetrates into the filfures expanding with fuch force during con- gelation, as to break off the corners and pro- jections. The fame circumftance is fometimes taken ad- vantage of in fplitting flate. The Collyweftern flate is dug from the quarries in large blocks, thefe are then placed in an oppofite direction to what they had in the quarry, and the rain is allowed to fall upon them; it penetrates the fiffures of the flate, and the firft {harp froft freezes the water, which, expanding with its ufual force, fplits the flate into thin layers. The benefit that a froft is known to afford to ploughed land, is effe&ed by the expanfion pf the water breaking and crumbling down the clods of earth. The expanfion of a Jolid body by heat may be inftanced in iron, and other metals. It a cylin- der of iron, that exactly fits a ring, fo as juft to pafs through it, be heated until it becomes red hot, it will not then pafs through the fame ring; but if you immerie it in cold water, or wait till it is EXPANSION BY HEAT. gradually cooled, it will pafs through the ring again with the fame facility as before. This faff is taken advantage of by coopers in fattening the Haves of a cafk with iron hoops; they heat the iron hoops, and of courfe enlarge them, before they put them on, that in cooling they may contraft, and tighten the cafk. In time-pieces this expanfion of metals is thfc caufe of flight errours; the vibration, or time of oscillation, of a pendulum is regulated by it’s length; the longer the rod the flower the vibra- tion; in the fummer, therefore, the rod being lengthened by the heat, the pendulum ofcillates lefs quickly, and the clock goes flower than in winter; and this is the cafe, with all clocks made in the ufual way. To reftify this errour, time- pieces, intended to be very accurate, are made with what is called the gridiron-pendulum, which is invented on the principle that different metals are expanded by heat in different degrees. Brafs, for inllance, expands twice as much, and zinc three times as much as iron by the fame increafe of temperature. In the gridiron-pendulum, there- fore, there are two rods of different metals, coa- nefted by a crofs-bar, fo proportioned in length, and fo difpofed, that the expanfion of the one (hall elevate the weight in the fame proportion as the expaniion of the other tends to depieis it; the pen- dulum therefore conflantly remains of the fame C 3 30 . II R A 1 IN PARTICULAR. length, and the effeChs of expanfion or contraction in the rod are counteracted. In the glafs manufactories the expanfion and con- traction of glafs by heating and cooling is a frequent fource of inconvenience and expenfe. It is natu- rally a very fragile article, and if cooled or heated very fuddenly is known to crack, and break to pieces; hence the necefiity of what is called anneal- ing, which is the expofing of new made glafs to be very gradually cooled. If heated glafs is fuddenly cooled, the external furface, having a tendency to contraCt whillt the in- ner parts remain in their expanded ftate, is neceffa- rily ruptured in the fame way that a bladder filled with air, when wet, will be cracked in drying by the exertion of its particles to contraCt, whillt the’ air within remains in the fame ftate of expanfion. If the annealing of glafs be not well performed, the particles on the furface may be contracted fo much more, than thofe of the internal parts, as to give the glafs an irregularity in its texture, but not fo much fo as to caufe a fraCture. Such glafs ap- pears found, and is therefore faleable; but is ever after lefs able to bear fudden alternations of heat and cold. This is the caufe why fo marry v glafs veffels crack the firft time that hot water is poured into them, or that they are otherwife expofed to fudden heat. The reafon why glafs breaks by the too fud- den application of heat is, that the particles of the EXPANSION BY HEAT. Si furface being more heated expand more than thofe of the inner parts, and in their tendency to feparate produce a frafture. Several ingenious modes of breaking glafs in any required direftion, fuch as are p raft i fed by chy- mifts, are founded on this circumftance ; by which means glafs veflelsthat are broken may be fafhioned and fitted for a variety of ufes. One mode, as pointed out by Mr. Henry, is to dip a piece of thread or firing in fpirits ol turpentine ; wrap it round the glafs in the direftion that you re- quire it to be broken in, and then fet fire to it. Another mode is, to draw a red hot fkewer acrofs the glafs in the delired direftion ; and a third is, to wrap a red hot wire round the glafs, and it it does not immediately crack, to throw cold water on it, whilfl the wire remains hot. The two former modes depend upon the fudden expanfion, and the laft upon the fudden contraftion of the particles on the furface of the 'glafs. The expanfion of fluids by heat is much greater than that of folids. It is made very evident by heating fpirits or any other fluid in a glafs veflel, that has a long and narrow neck ; as the heat is in- creafed the fluid is expanded, and it confequently rifes in the neck of the veflel. This expanfion of fluids has been very ufefully applied in the conftruftion of thermometers, by C 4 22 HEAT IN PARTICULAR, which it is made the means of meafuring the va- riations of heat in other bodies. In the thermometer, which is an inllrumeni fo common as to need no defcription, the liquor con- tained in the tube is expanded by heat, and con- trailed by cold, and confequently rifes and falls ; which rifrng and falling is rendered very fenfible to Lhe eye, by making the bore of the tube, which may be compared to the neck of the yeffel in the former experiment, very fmall in proportion to the bulb, which may be confidered as the body of th$ veffel. This tube being applied to a fcale, formed on fixed principles, the rife and fall of the liquor with- in it is meafurcd with accuracy, and thus becomes the true fignof the increafe or diminution of temper rature in any fubftance, to which the bulb of tho thermometer is applied. It does not however indi- cate the real quantity of heat in fuch fubftances, but only fhows that one body is warmer than another, and by how many degrees of heat the temperature of the one exceeds that of another. When a thermometer is immerfed in water, which caufes the mercury in the tube to ftand at the fiftieth degree, and then into water, which raifes it to a hundred, it is a common expreflion to fay, that the latter water is twice as hot, or contains twice as much heat as the former ; and thus Sir EXPANSION BY HEAT. S3 Ifaac Newton talks of boiling water being three times as hot as the blood in the human body. This however is an errour, and it arifes from the idea, that the fcale of the thermometer commences *t the point, below which there is no heat. Thus Newton believed the freezing point to be the natu- ral zero, below which there was no heat ; whereas we now know, that the freezing point is feveral de- grees above the temperature of the air at certain fea- fons in the polar regions, as in Hudfon’s Bay, or at Kamtfchatka. In the latter place mercury has frozen by expofure to the natural cold, fo that the air at fuch time mull have been at leaft 40° below the zero of Fahrenheit’s fcale, or 72° below the freezing j)oint. By artificial means flill more in'tenfe cold than this has been produced, and yet we have no reafon to believe that we have reached the low ell point, or that of the privation of all heat. The range of heat from its loweft to its higheft degree may be aptly compared to an immenfe chain, formed of links, that have exactly the fame length, the extremities of which chain are beyond the li- mits of our fight. The moft diftant link, that we can diftinguifti towards one extremity, we mark as the firll, that next to it the fecond, and fo on, till we come to the moll diftant that we can diftinguifh towards the other extremity. Now in fpeaking of the links of this chain, which may be compared to C5 Sh HEAT IN PARTICULAR. the degrees of heat on the fcale of a thermometer, it would evidently be erroneous, to fay, that an objeft placed at the hundredth link was twice as far from the extremity, as one placed at the fiftieth; nor could we fay how far either was from the ex- tremity ; but knowing that there are fifty links be- tween the two, we can form an idea of their dif- tance from each other, and their relative fituation with refpeft to other, objects placed along the fame chain, that are within our view. So, with refpeft to the thermometer, we know the number of degrees between the temperature of boding water and of ice ; and that the. former, which is at 212°, is as much hotter than water at 122° y as this is hotter than ice, which is at '32°, there being 90° between each. Thus then the ther- mometer teaches us the relative,, but not' the abfo- lute heat of bodies. The tube of the thermometer is fometimes filled .with air, fometimes with fpirits, and fometimes with mercury. The air thermometers, being molt delicate, are ufed in fome chymical experiments; as the air is expanded or contra&ed in thefe thermo- meters, a coloured liquor is made to fall or rife, which marks the degree of expanfion, and confe- quently the variation of temperature. The fpirit-thermometers are applicable to infenfe degrees of cold, j^ecaufe the fpii it will not freeze where the mercury would ; but they will not anfwer EXPANSION BY HEAT. 35 for fucli high degrees of heat, the fpirit being fooner evaporated. For ordinary ufe and for moft chymi- cal experiments the mercurial thermometers are to be preferred, anti principally for this reafon, that mercury is equably affeiled by equal increments of heat at different temperatures, which is not the cafe with fpirits, and flill lefs fo with air. Thermometers, from their conftruilion, are nqV calculated tomeafure very high degrees of heat; the tubes would be broken, and the mercury would be volatilized, if they were expofed to much heat. To anfwerthis purpofe other contrivances have been offered. Some thought that the expansion of me- tals would furnifh a convenient meafure, others propofed the rate at which metals cool, as a meafure of their former temperature; but none can be com- pared in accuracy to the pyrometer invented by Mr. W edgwood. Noticing the contraClion of clay in baking, he found that it contrails uniformly according to the degree of heat; and if the fame kind of day is ufed, that its contraction becomes an accurate meafure c£ the temperature. His pyrometer confifrs of a number of fmali pieces of {lightly baked clay, and a brafs plate with two rulers, io fixed to it, that they gradually ap- proach each other. On this plate is a fcale of de- grees, made to correfpond with thofe of Fahrenheit's. a he firft degree of the pyrometer ewefponding Ce HEAT IN PARTICULAR. with 1077§° of Fahrenheit’s, and each degree after- wards equalling 130° of Fahrenheit’s. The pieces of clay are all of a size, and fit in, between the ru- lers, where the firft degree is marked. When this infrrument is ufed, one of the pieces is expofed to the heat required to be afcertained, that of a furnace for inftance; and when it has been ^expofed ' long enough to have acquired the heat of the furnace, it is withdrawn, cooled, and then ap- . * plied to the rulers, between which it is allowed to Hide as far as its bulk will admit it. The degree ^marked at the place, where it flops, indicates the temperature of the furnace ; for the greater that has been, the more will the clay be confcrailed, and confequently the further it will Aide between the converging rulers. Before we quit the fubjeil of expanfion of fluids by heat, we muft notice the peculiarity of water in this re r pe£l. Within a certain range of temperature ' water follows the general law of being expanded by heat, and contrafted by cold ; but beyond this, it is affeiled in the oppofite way. When heat is applied to water at 32 ° it gradually contrails till it arrives at 40°, whereas other bodies expand in the fame fiiuatibn; but after it .arrives at 40°, it follows the general law, and is dilated by the further appli- cation of it. When boiling water is gradually cooled, it regularly contrails, imtil it arrives- again EXPANSION BY HEAT. $ 7 at 40°, and then it fhows its peculiarity, and is ex- panded as it is further cooled. The final caufe of this peculiarity is to prevent the fudden congelation of large maffes of water, and to preferve a warmth in feme part of the water of lakes, and rivers, that may hap port the life of its various inhabitants. How it effe6ts this, isr thus explained. •, Water never freezes until its temperature is re- duced to S2°. When the particles of water are expanded or contrafded by variations in their tem- perature, they become fpecifically lighter or heavier than the furrounding particles, and confequently r ife in the former and fink in the latter cafe. When therefore the water of a lake, which is at 60°, is gradually cooled by the approach of winter, the particles on its furface, being firft cooled, con- tra£i, become fpecifically heavier, and therefore fink. Their places are fupplied by others, which are cooled, contrafled, and fink in the fame way ; and thus the whole body of water is gradually cooled. This procefs would continue, were it not for the peculiarity we have been fpeaking of, till the whole body of water had; been funk to the tem- perature of 32°, and then the whole would be fud- denly frozen ; which would prove certain defiruc- tion to all the animals it contained. This would be the cafe, did water expand and -Contxafl by heat like pther fluids ; but now, as foon 58 HEAT IN PARTICULAR. as the water of the lake is all cooled to 40*, the particles on the furface no longer contraft, but on the contrary expand ; they are confequently lighter than the particles below, and therefore remain at top, and are Itill further cooled till they come to 52°, and then ice begins to form. Ice being but a bad conduftor of heat, the pro- cefs of cooling now goes on very {lowly in the water; and whilft the air and ice are cooled, per- haps far below 32 °, the water, under the ice re- mains even at 40°, or little below. This wife provifion of nature, which anfwers fuch an important end, is confined to frefh water. That of the ocean being prevented from freezing, except in the polar regions, by its immenfity, its communication with waters of warmer climes, and by its containing fait, which enables it to be reduced below 32 ° without freezing, needs not this pecu- liarity of expanding after its temperature is reduced to 40°. The water of the ocean therefore expands and contrafts according to the general law, and this again is attended with confiderable advantages. It being neceffary that the whole body of water fhould be equally reduced in temperature, that on the furface is feldom cooled fo low as 32 °, and is therefore, in the winter time, warmer than the at- mofphere, to which it becomes a confiant Tource of heat. The winds in palling over the ocean ac- quire warmth, and moderate the cold of. the atmof- I EXPANSION BY HEAT. 39 phere on the land to which they blow ; and this is the reafon why i hands are more temperate than parts of the continent fituated in the fame latitude. The expanfion of gaffes, airs, or gafeous fluids, by heat, may be inilanced in the fimple experiment of holding a half-blown bladder before the fipe. As the air in the bladder becomes heated, it ex- pands, and what before only half filled it, now dif- tends it to the utmoft. It is by this expanfion of air by heat, that heated bodies are enabled fo readily to part with their heat to furrounding ohjefts, and that fo juft an equilibrium is maintained. When any part of the air is heated by the fun’s rays on the earth, or by any heated body, it becomes expanded, and of courfe afcends, whilft other par- ticles of air rufh in to fupply its place. Thus heat is tranfmitted from one place to another, and be* comes more equally diffufed. This is one caufe and the principal caufe of winds. When the atmofphere in any particular country is heated, as in the torrid zone, the ex- panded air afcends, and currents of cooler air rufh in on all Tides to fupply its place. Thefe currents form the monfoons and trade winds, which blow regularly in certain latitudes, and at ftated times. The draughts of air perceived in rooms, where there are fires, are currents of air rufhing in to fupply the place of the expanded air, that paffes up die chimnies. It is by facilitating the egrefs of 40 HEAT IN PARTICULAR. the heated air, that rooms are properly ventilated ; and by contriving means to prevent its efcape, that floves and hot-houfes are able to preferve their in- creafed temperatures* 41 ESSAY V. EFFECT OF HEAT IN CONVERTING SOLIDS INTO FLUIDS, AND FLUIDS INTO VAPOUR. * We now come to the fecond general effefl: of heat ; its power of changing the form of bodies by converting folids into fluids, and fluids into vapour. Moll: fubftances are capable of being thus melted, and vaporifed by the application of heat ; and moll probably all would be fo, were we able to excite a fufficient degree of heat. By abftra6ting the heat, we again reduce moft vapours to their fluid ftate, and fluids to that of folids. And it is like- wife probable, that fuch as at prefent we cannot condenfe, or freeze, would be fubjeft to -thefe changes, were we able to excite a fufficient degree of cold. It is only when the temperature is raifed to a certain degree, that folids begin to melt, or fluids to be vaporifed ; and this degree is different lor every different fubftance, but is always precifely the fame for the fame fubftance, provided other circumftances are fimilar. Thus ice always melts when heated above 32 °, as water always freezes when cooled below 32 0 ; and water is always con- 4:2 EFFECT OF HEAT* verted into vapour when its temperature is raifed to 212°, provided the preffure of the atmofphere is the fame. Wax has another degree at which it is melted, lead another, filver another, and gold another, The degree of heat, at which fpirits boil, or begin to be converted into vapour, which is the fame thing, is lower than the boiling point of water ; and that, at which aether boils, is a great deal lower hill. The point, at which fait water freezes, is lower than the freezing point of frelh water ; and in the aft of congelation its fait is depofited ; and the ice, if feparated and melted, affords frefh water. Some of our navigators have obferved this fa£t with great joy, and- obtained a fupply of frefh water, where they but little expefled to meet with it. The mountains of ice met with at fea in the polar re- gions are wholly of frefh water, and^ pools or ba fons of frefh water are often found on them from the partial melting of the ice. Although all thefe fubftances have their fixed points, at which they boil under fimilar circum- ilances, yet the preffure of die atmofphere has a very confiderable influence in determining the point. The greater the preffure the greater the degree of heat requifite for making the liquor boil ; and the more we can diminifh the preffure of the atmofphere, as is done by the airpump, the lefs is EFFECT OF HEAT. the degree of heat that is required to convert it into vapour. In this way aether, {pints, and even water, are I made to boil at the ufual temperature of the air, when the prelTure of the atmofphere is removed by means of the airpump. So much is the boiling facilitated by this means, that phiiofophers have gone fo far as to affert, that, if all preffure Was removed from the earth, every fubflunce, folid as 1 well as fluid, would immediately be volatilized, or converted into vapour. For further obfervations on this point we fhall confine ourfelves to the confideration of water, as its influence on this fubflance is mofl attended to. Water, upon an average, is found to boil at £12°, and this is generally confidered its boding point ; but in this country the*e is a confiderable dif- ference at different times in the weight of the atmofphere. In the barometer, which is the in- ftrument for meafuring this preffure, the height of the mercury varies as much as three inches, and a rife of one inch makes the water require two degrees more of heat to boil it. There is therefore in this country a variation of fix degrees of heat in - the temperature of boiling water at different times. ■'When the barometer is at the loweft, water will boil at 209°; and when it is at the higheft, it will not boil till it is heated to 21 5°. The more elevated the fituation, the- lefs is the 44 - EFFECT OF HEAT* prefTure of the air, and confequently water will boil with lefs heat on the top of a mountain, than in the valley. An amufing experiment, eafy to be performed, which I {hall now defcribe, fhows this effeft of prefTure on the boiling of water, as well as any experiments that can be performed with the air- pump. Half fill a Florence flafk, or other glafs veffel, with boiling water, and cork it tightly. The water is now at reft ; but pour a little cold water on the upper part of the flafk, and it will begin to boil ; then pour hot water upon it, and it will ceafe ; pour the cold water again, and it will boil ; and fo on, for a confiderable time. The explanation of the experiment is this. When you cork the flafk, the upper part of it is filled with vapour from the boiling water, and the cold water poured upon this part condenfes the vapour. Now as the air cannot get in, there is a partial va- cuum ; that is, the prelfure of air on the furface of the water is confiderably diminifhed. This being the cafe, the water will boil at a lower tem- perature ; and the heat, which it retains, is fuffi- cient for the purpofe. In the next place, by pouring hot water upon it, that within is partly again converted into vapour, which affords the fame prefTure as the air would do ; the water therefore ceafes to boil, becaufe its heat is infufficient und$r that prefTure to make it boil. EFFECT OF HEAT. 45 It has been faid, that, by increffing the preffure on the furface of water, you retard i s boiling. It is on this principle, that what are called digejiers , are formed. By means of fcrews, the top of the veffe*l is kept down with fuch force, as to prevent the efcape of the vapour, which increafing the prefTare on the furface of the water, in the fame degree enables it to acquire a higher temperature. Papin carried his to that pitch, that the water ac- quired a fufficient degree of heat to melt lead. A veffel on the fame conftruftion, but of far lefs power, is now introduced into the kitchen with economical views. By enabling the water to be heated much above the boiling point, its folvent powers are increafed ; and thus bones are made to afford their glutinous and nutritious parts to the water, that common boiling would not be able to extra#. The immenfe power that is exerted by water, on the point of being converted into fleam, re- quires digefters, and other inftruments, intended to confine it, to be made with great care, and with amazing flrength. By a fufficient increafe of heat it may be made to exert almoft any force. It has been made to burft cannons, and ftill ftronger machines ; and by the important invention of the fleam engine, it is- brought to move very heavy weights. 46 EFFECT OF HEAT. When a fub fiance undergoes the change that we have here been talking of, from folid to fluid, or fluid to vapour, it is not only neceflary to raife its temperature to the melting or boiling point, but to fupply it with ff ill more heat, for the converfion is attended with an abforption of heat. When ice is melted it abforbs heat from all fur, rounding bodies, ^hich heat has not the effe£l of increafing its temperature,' but becomes latent ; the water is not hotter to the feeling, or to the ther- mometer, than the ice was, before it was melted, but it has abforbed and contains more heat. The fame happens, when a fluid is converted into vapour ; and the fame quantity of heat, that is thus abforbed, is again extricated, when the va- pour is condenfed into a fluid, or the fluid frozen into a folid. The application of this fa£t aflifts us in explaining a variety of phenomena, that without the knowledge of it would be inexplicable. Put a veflel of fnow or of ice before a fire, and although it is all the time receiving heat from the fire, a thermometer immerfed in it fhows no increafe of temperature ; all the heat, that is received, being neceflary to convert the fnow into water : but as foon as it is all melted, the thermometer begins to rife. Were it not for this circuxpflance, all the fnow and ice would be inftantly melted, when the tem- 47 EFFECT OF HEAT. perature of the air is raifed above 32 °, the confe- quence of which would be dreadful inundations after every winter. So much heat is abforbed when a folid becomes fluid, that if we can fuddenly effett the converfion, we produce a great degree of cold, and on this de- pend the efife&s of freezing mixtures. When fnow and fait mixed a^e melted in a warm room, fo much heat is abforbed by them that a veffel of water immerfed in the mixture becomes frozen, notwithftanding the warmth of the room. In this way our confeftioners prepare different kinds of ices in the fummer. Various mixtures of falts, when diffolved in water, produce the fame effe£l without the addition of ice. Eleven parts of fal ammoniac, ten of faltpetre, and fixteen of Glau- ber’s fait, mixed with thirty-two parts of water, will produce a cold fufficient. to freeze water. By diffolving muriate of lime in nitrous acid even mercury may be frozen. The heat that is given out, when water is frozen, tends to moderate the intenfity of our winters, and accounts for the increafe of warmth that is fre- quently obfervable after a fall of fnow. Other fluids give out heat during their converfion to a folid ftate. In falls it may be initanced by the following experiment. Boil a pound of Glauber’s fait in a pint of water, and when boiling hot, pour fome oi this faturated folution into a phial, but 4$ EFFECT OF HEAT. not fo much as to fill it ; cork the phial clofe, and let it ftand to cool. When cold, the folution is Hill fluid ; but the inftant you draw the cork, the fait becomes cryflailized, and the whole niafs folid, and at the fame time fo much heat is evolved, as to make the phial very fenfibly warm. This is an in- fiance of heat being given out by a body during its converfion from a fluid to a folid ftate. The explanation of the experiment is this : water will dilTolve more Glauber’s fait when hot than when cold ; and cold water will diffolve more in proportion as the preffure of the atmofphere is dimi- nifhed. The hot water was here faturated, and would, if fuffered to cool in an open veffel, have depofited part of the lalt; but by corking it. when hot, the fuperior part of the phial being filled with vapour, would form a partial vacuum on the furface of the folution, when by cooling the fleam was con- denfed. The preffure of the atmofphere being thus diminifhed, the cold water was able to retain in fo- lution all the fait that the hot water had diffolved ; but as foon as by drawing the cork you admitted the ufual preffure of the atmofphere, the cold water was rendered incapable of holding fo much fait in folution, and part was inftantly cryflailized. When fluids are converted into vapour, I have faid, that there is much heat abforbed, and of courfe cold produced. This takes place both when they are vaporifed by heat, and when they are raifed 4 effect of heat. 49 by what is called fpontaneous evaporation ; which procefs differs from the former in other refpe&s, though it agrees in this. When aether, fpirits, or water are expofed to the air, they are gradually evaporated, and in this pro- cefs abforb heat, as well as when they are made to boil and are thus vaporized. To prove this, dip the bulb of a thermometer in aether, and expofe it to the air, and you will find the mercury to fall confiderably ; or dip your hand into the fame li- quor, or into fpirits, or even water, and then ex- pofe it to the air, and you will feel a very confide- rable degree of cold, in confequence of its' abforb- ing heat from your hand to convert it into vapour. In warm climates the inhabitants cool their water, and other liquors for drinking, by wrapping the veffels in wet rags, and fufpending them in a cur- rent of air ; or by keeping their water in porous earthen veffels, through which a part gradually oozing is evaporated, and cools the reft. It is this evaporation that makes a perfon feel fa cold when his clothes are wet, although he is per- * haps fitting near a fire ; and it is the cold thus pro- duced that injures the health much more than being expofed to a cold and fharp air. It is the abforption of heat by the vapour that prevents water from ac- quiring a greater degree of heat than 212 °. If you boil water ever fo violently, or apply to it ever fo rntenfe a heat, it never increafes in temperature; D 50 EFFECT OF HEAT. the heat that you communicate all going to the coil- verfion of it into vapour. In cooking therefore it is ufelefs to apply additional heat to water that is boiling, to make it, as the fervants call it, boil faff. If you keep the water boiling at all, that is fuffici- ent ; and in many cafes indeed articles will be as well done, and as foon done, by a heat confidera- bly lefs than that of boiling. Having obferved that vapours contain more heat than fluids, and fluids than folids, when their tem- perature is the fame, I mull now add, that among fluids, among folids, or among vapours, one kind contains more heat than another ; thus a pound of water contains more heat than a pound of mercury ; a pound of iron more than a pound of tin ; and a cubic foot of common air more than the fame quan- tity of inflammable air. According to the proportion that different bodies poflefs, fuch we fay is their capacity for heat ; thus we fay that water has a greater capacity for heat than mercury, and iron than tin. The confequence of this difference of capacity is, that different bodies expofed to the fame heat require different times to be raifed an equal number of degrees ; thus, expofe the fame quantity of mercury and of water to the fame heat, and the former will be heated 8°, 10°, or 12 p , long before the water, becaufe it requires a lefs quantity of heat to raife it. 6 EFFECT OF HEAT. 51 In chymical experiments, whenever there is a change of capacity without a change of temperature, there is fure to be a fudden evolution of heat, or abforption of it producing cold. Thus on mixing fpirits and water, and ftill more on mixing vitriolic acid and* water, a very fenfible degree of heat is evolved, becaufe the mixture has lefs capacity for heat, than the two feparately. So the heat produ- ced when fluids become folid, and the cold when they become vapours, as mentioned above, is ex- plained by the folid having a lefs and the vapour a greater capacity for heat than the fluid. All the heat afforded by combuftion of inflamma- ble bodies is given out, in confequence of the re- fult of combuftion, as the afhes,' fmoke, &c., hav- ing a lefs capacity for heat, than the combuftible body, and the air that has been confumed^. There is another law of heat that requires to be mentioned, viz. that it paffes more readily through one fubftance than another ; and this quality in the fubftance to tranfmit it, is termed its conducing powers If you hold a glafs tube and a piece of wire with your hand in the flame of a candle, you will foon be made fenfible that the wire is the heft conduftor. Air, when confined, is a bad conduc- tor ; and this is the reafon why all porous bodies are fo. Wool, by admitting and confining particles of air in its interftices, is a very warm covering for the D 2 EFFECT OF HEAT. animals that bear it, and a warm clothing for man. Double windows and double walls make the warmeft rooms in cold climates, and the coolefl in Warm climates; for the air enclofed between them, being a worfe conductor than either wood or ftone, prevents the egrefs of heat in the cold, and its in- grefs in the warm climates. For the fame reafon partitions made with lath and plafter, with an inter- mediate fpace, make the’ rooms in this climate war- mer than wainfcot partitions. In hot-houfes not only the walls but the fafhes Ihould be double., to retain the heat moft effe&ually. Snow being a light porous body is a bad conduc- tor of heat, and on this account is of infinite fer- vrce in preferring vegetation ; for let the air be ever fo cold, the ground, that is covered with fnow, is feldom reduced in heat below 32 ° ; and this ac- counts for animals living fo long, that are buried *n the fnow. 63 ESSAY VI. COMBUSTION. The third and laft general effeft of heat is combujiion. When a body, that is not very inflam- mable, is heated to a certain degree, it becomes luminous, as iron for inftance, and is then faid to be ignited, or to be in a {fate of incandefcence r but when a more inflammable fubftance is heated, it undergoes a procefs called inflammation, during which heat and- light in a greater proportion are emitted, and the chymical qualities, both of the inflammable body and of the furrounding air, are materially altered. Incandefcence is probably the fame procefs with inflammation, only in a flighter degree, and we (hall confiuer both under the term combuf- tion. The combuflible body in common language is faid to be confumed; but it muff not be fuppofed that it is annihilated, that it is abfolutely deftroyed, for in faft it is only changed; and the refults of combuf- tion are always equal in weight to the inflammable body, and the air abforbed. It ought here to be obferved, that inflammation or combuftion can never take place without air, D s 54 * COMBUSTION. If an ounce of phofphorus is confined in a vefle! of air, and the whole apparatus weighed, and if you then fet fire to the phofphorus, and let it burn until it is, to fpeak in common language, all confumed, the apparatus, on being again weighed, will be found to have neither loft nor gained by the experiment. A change however has taken place, the volume of air is diminifhed, and the phofphorus is converted into an acid; which acid, if weighed, will be found equal to the phofphorus that has been burnt, and the air that has difappeared. Similar fafts will be afcertained in every inftance of combuftion. There is a chymical change, but no abfolute lofs or confumption. If the whole produfts were collefted after a candle is burnt out, or after the combuftion of any kind of fuel, they would always be found to equal in weight the in- flammable body and the air, that feem to have been confumed. As the prefence of air is an effential requifite in every cafe of combuftion, and as it always undergoes a chymical change, it is probable that it is the fource both of the heat and light that are extricated. Of the heat indeed we know it to be the chief, if not the only fource, in confequence of the change of capacity that attends its chymical change. The vulgar opinion, therefore, that the fuel gives out the heat, and the candle the light, is erroneous; audit is an inaccuracy in language to COMBUSTION. 65 fay, that one kind of fuel gives out more heat, or one kind of candle moire light, than another. As, however, the errour and the inaccuracy can be the caufe of no inconvenience, it would at leaf! be ufelefs in common converfation to make ufe of other terms. As air is thus neceffary to combuflion, great attention to procure a fufficient fupply becomes a point of confiderable confequence in promoting and keeping up the procefs. In conftruiting furnaces, and even in fitting up fire-places, it requires the chief confideration. In the former, the length of the chimney in a great meafure influences the heat, by caufing a greater or fmaller current of air through the fire; and dampers or regifters are in fome cafes ufed, which, by admit- ting more or lefs air into the furnace, regulate the intenfity of the heat. The ufe of bellows depends on their fupplying a greater quantity of air; and in the furnaces of iron-foundries immenfely large bellows are ufed to increafe the draught. In common fire-places, the dimenfions of the chimney, the pofition of the flove, and the free acceffion of air, are the three points chiefly to be attended to, with a view of having good fires, and preventing the inconvenience of fmoky chim- nies. When the chimney is very large, as mofl kitchen chimnies were formerly built, they are D 4 66 COMBUSTION. aimofl fure to fmoke. The column of air in the chimney not being all fufficiently heated to afcend, there are different currents ; the heated air afcends in the middle, whilfl the colder air defcends at the hde$, and in defcending forces part of the fmoke with it into the room. To prevent this, the fire is made larger, and the door, or a window, is opened; the heat now is fufficient to expand all the air in the chimney j but if the door or window is ngt open, there not being a fufficient quantity of air admitted by the ufual crevices, the external air forces itfelf down the Tides of the chimney to fupply the place of that which is con fumed, and that, which being expanded, paffes up the middle of the chimney, and thus the fame inconvenience is repeated. By contracting the throat of fuch a chimney, the column of air to be heated is lefs, and is fuffici- ently expanded by lefs fuel, at the fame time that the current of air required to keep up a brifk fire, is lefs; fo that the chimney will no longer fmoke, nor does the neceffity of opening the door exift. If a flove is placed very forward in the room, the heated air a expanded, and afcends in the ■ retment, and the fmoke along with it, pa tic li- ke fire is firfl lighted ; the air in the . : en g then not heated fo as to eflabliffi a This is often obferved in old-falhioned COMBUSTION. 57 moveable fire-grates, and is generally remedied by pufhing them a little back warder. The free acceffion of air is the moft important con fi deration. We have feen, that without it a current of air will be formed down the chimney that mull inevitably bring the fmoke with it. In fmall and clofe rooms it is the moft frequent caufe of fmoky chimnies and bad fires. When it is found, that opening a door or window prevents the fmoke from defcending, the caufe is evident, and the cure is generally accomplilhed by con- triving a communication with the air; and if this can be done under the grate, or near it, fo much the better ; as a current of cold ^ir from a diftant part of the room will be fure to prove inconvenient. If the room is lofty, a communica- tion may be made over the door or near a window, above the height of perfons in the room, which will prevent any inconvenience from the current. But m low rooms, I have feen this attempted and fail; or it has anfwered only when the fire is firft lighted, or before the air in the room has been heated by company. The reafon of this becomes clear and evident, if a candle is held before the opening, at a time when the air in the room is heated ; for the flame of the candle is drawn towards the opening, and not from it into the room; which proves clearly X) 5 58 COMBUSTION. that, inflead of admitting air, it is the channel through which air is carried out of the room. Many chimnies only fmoke when the fire is firfl lighted, which arifes from the air in the chimney being colder than the external air; in confequence of which it defcends, and, palling through the fire, carries the fmoke with it through the bars into the room. . This mayv be prevented by laying the fire very light, and fetting fire to a handful of fhavings ©n the top previoufly to lighting the fire at the bottom ; or more certainly by fetting fire to a piece of paper, and holding it a little way up the chimney. This heating the air in the chimney is fure to eftablifH a current in the proper dire£lion, and carry the fmoke upwards. Mofl chimnies are in this predicament when fires are lighted for the firfl time after a long interval, as in the beginning of winter ; and ignorant people attribute it to the air in the chimnies being damp. The fa£l is, that the air in the lioufe, and confe- quently that in the chimney, is colder than the external air, as is the cafe during fummer and autumn, until by lighting fires we have increafed its temperature. The firfl time a fire is lighted, therefore, as the air in the grate is expanded, its place is fupplied by cold air from the chimney, which ru filing through the fire carries the fmoke into the room, unlefs, as I have before advifed, COMBUSTION. 59 fome means are taken firft to warm and rarefy the air in the chimney. Argancl’s lamp burns better than a common one becaufe it admits a current of air through the centre of the wick. This caufes fo complete a combuf- tion, that the fmoke, which oil ufually gives out, is burnt in this lamp, and therefore it affords more light. When we wifh for light rather than heat, we employ fuch inflammable fuhftances as allow their particles to be volatilized, as fpirits or oils ; for flame is part of the inflammable fubftance vola- tilized by heat, and flill in a Hate of combuftion. It is always conical, and its external furface only is in an ignited hate, as is eafily proved by fud- denly thru fling a match into the centre of the cone, as of that arifing from fpirits burning in a (hallow difh. If you allow it to remain there fome time, and then fuddenly withdraw it, the brimftone on the end of it will not be burnt. The reafon why only the furface is in combuftion is, that the contaft of air is neceffary, and it has no accefs to the centre. We have now gone through the confideration of the general effects of heat, and taken notice of its laws refpefting inanimate matter. It is by attending to all thefe properties that fo much has of late been done towards economifmg fuel * and D 6 60 COMBUSTION. Count Rumford is the perfon to whom we are indebted for molt of thefe improvements. That patriotic and humane philofopher has Ihown the true value of literary acquirements, and taught us the juft application of philofophical truths, by making them fubfervient to the relief of the poor, and to the benefit of his country. In cooking he has taught us to economife our fuel, by applying feparate fires to the pots or boilers, to the ovens and roafters, and to fmaller utenfils, as kettles and faucepans. In a kitchen range, as commonly fitted up, nine tenths of the heat is either carried up the chimney, or ufelefsly thrown into the kitchen, to the great inconvenience of the cook. If all this heat, that is loft, could be faved, or applied to the intended purpofes, one tenth of the fuel, that is now ex- pended, would be found fufficient, and confe- quently the faving would be immenfe. ' The improvements, which I am about to notice, do not lay claim to fo much as this, but have cer- tainly accompliftied much. The chief object is to confine, as much as poffible, the heat emitted to the v fe for which it is intended, namely, boiling, roafting, ftewing, &c. ; which is only to be done by uling clofe ftoves, and applying the fire feparately to different veflels. It will be unneceffary to detail minutely all the methods he has adopted to effefl 5 COMBUSTION. 61 this purpofe. The leading principles of his im- provements will be made evident by the following obfervations. When in the common mode of cooking, where the kitchen is furnifhed with a range, you wifh either to roaft or boil a joint of meat, it is requifite that the fire fliould be made up, as the cook terms it, long before he can lay down the meat or put on the boiler. That is to fay, in faft, that it is ne- ceiTary to heap on an immenfe quantity of coals, and fuffer them to burn till the fire is clear and bright, before the heat can be applied to the re- quired jpurpofe ; and even then it is but a fmall proportion of the heat given out, that you can ap- ply either to boil the water in the pot, or roaft the joint upon the fpit. If you are boiling, for example, all the heat that emanates from the burning fuel in front of the fire is completely loft ; and only that, which rifes from the top, and direftly ftrikes againft the pot or boiler, goes to anfwer the intended purpofe, which cannot upon an average be fo much as one tenth part of the whole heat afforded by the combuftion of the fuel. This mode of boiling upon an open fire, too, makes it neceffary to have the kitchen ranges very deep from front to back, which adds confiderably to the confumption of fuel. In the next place, when it is required to roaft COMBUSTION. m at one of thefe fires, all the heat that emanates from the top of the fire is decidedly loft ; and of that which comes from the burning fuel in front, only fuch a part, as is direftly oppofite to the meat to be roafted, is appropriated to the intended purpofe. In mo ft kitchens, a fmoke-jack, and in many an iron oven, fitted up by the fide of the range, and heated by meahs of a flue going from the back of it to the oven, are part of the cooking apparatus. The plaufibility of the jack being made to aft, and the oven to be heated, without an additional fire, has perfuaded moft people to believe them very eco- nomical contrivances; whereas, if duly confidered, they will prove to be very extravagant ones, adding confiderably to the expenditure of fuel. To ereft one of thefe fmoke-jacks, it is neceflary that the chimney be very large ; and to put it in motion, it is requifite that the whole column of air contained and palling through this large chimney be conftantly heated, not only fufficiently fo to carry up the fmoke, but to produce fuch a current as will keep this badly- contrived machine in motion. To effeft all this, a much larger fire mull be made, than would be required merely to roaft the meat, particularly if it is a fmall joint ; for if the fire be reduced, the fmoke-jack Hands Hill. Befides this unneceffary exhauftion of fuel, al- moll every fireplace thus conftrufted is found td COMBUSTION. 63 fmoke, unlefs the door or windows be kept open,, and a brifk fire kept up ; fo that fuch apartments cannot be preferved uniformly warm. To heat the iron oven, that I have fpoken of, it is requifite that a very brifk fire be kept up in the grate ; and from the length and awkward ftru&ure of the flue, in fuch as I have feen, the greateft part of the heat is loft and diflipated, before it reaches the oven. Another mode of applying heat to cooking, which is thought by fome a very great improvement, is by means of what is called a fleam-kitchen. This ap- paratus is very neat, and adds much to the conve- nience of the kitchen, as it is not neceffary to over- heat it by a large fire, as in the common mode of boiling. This plan, however, is found by no means to fave fo much fuel, as.. was at firft apprehended ; and when we confider how much apparatus is to be heated by the fleam, before it is applied to the defired purpofe, and ftill more, when we confider how much heat is abforbed, and rendered inert, as it were, in the converfion of water into fleam, we fhall be aware of the great fources of the lofs of heat in this apparatus. Having thus pointed out how, and why, the ufual modes of cooking are attended with confiderable wafte of fuel, it will, from what has been faid, immediately occur to you, that by ufing feparate fmall fires under the boilers, ovens, &c., moft of 64 COMBUSTION, the fources of this lofs of heat will be avoided. If -the coppers and boilers are well hung, and the ovens or matters well fet up, almoft all the heat afforded by the combuftion of the fuel is applied to them ; and, in confequence of the length of the flue, the current of, air through the fire is fo briik, as to confume cinder-afhes moiftened, or other fuel, that would hardly bum at all in open fire- places. The fame quantity of food may thus be cooked with not more than one fourth part as much fuel, as in the common way. As the machine called a roafter, a late invention of Count Rumford’s, is not yet become a part of the cooking apparatus, I fhall* offer a flight defcrip- tion of it. — It is fomething like the common iron oven, except that, inftead of being fquare, it is nearly cylindrical, flattened however at the bottom. It has a double door, with an intervening fpace of about an inch, to prevent the efcape and lofs of heat. There are two iron tubes running along its bottom, on the outer fide, which turn up at the back of the machine, and open into it, near the top ; the other orifices open into the kitchen, in front of the roafter, and immediately under it ; which orifices are furnifhed with plugs or ftoppers. Another part of the apparatus is a valve, {hutting or opening a communication between the roafter and the chimney of the flue. The grate, which fhould be very final 1, to prevent too large a fire COMBUSTION. 65 being kept up, is fituated immediately under the machine, and not more than fix inches below the tubes; which, with the bottom and fides of the roafter, are direclly expofed to the fire. When ufed, the meat is to be put upon a wire ftand, over a pan of fait and water, and placed either on the bottom of the roafter, or on a fhelf, which moft of them are made with, to allow of roafting two difhes at a time. The tfalve is now to be turned, fo as to prevent any communication between the roafter and the chimney; and the orifices of the tubes are to be clofed with their (toppers. The fire being lighted, the water in the pan is foon converted into vapour, and the meat is, as it were, parboiled. About twenty minutes, or hall an hour before you expect the meat to be fiifficiently cooked, the valve is to be opened, to let out the vapour ; and the Hoppers are to be taken from the tubes, that th.o gh them the roafter may be fupphed with hot and d.y air. The meat now begins to be browned, and to a (fume the appearance of roafted meat ; from which, when quite done, it can fcarcely be d\ftinguiihed by the niceft palate. It has not the peculiar flavour of baked meat, and for the plain reafon, that the fleam of the water prevents any vapour rifing from the meat in the former part of the procefs, and the opening by the valve prevents it's remaining in du- ring the latter part; from the confinement of which. 66 COMBUSTION. in the common mode of baking, I conceive the pe- culiar flavour of baked meat to arife. By putting the meat into the roafter before the fire is lighted, it becomes gradually heated, and hence retains all its juices; which makes the meat cooked in this manner particularly palatable. In- deed, on this point, the Count obferves, that the 1 mailer the fire, and the more flowly the meat is cooked, the better flavoured is it when done ; and what is of confiderable importance, the lefs luel be- comes neceflary. If the fire is fo fmal!, that a joint of meat requires fix or eight hours cooking, lefs fuel will be confumed, than if the heat is fufficient to cook it in two or three hours, and at the fame time the meat will be more palatable. The roailer likewife anfwers all the purpofes of an oven, by heating it before the bread or other things are put in, and by keeping the valve fhut, and the tubes always open. They may be made of any fize, but two fmaller ones are preferable to one large one. For a mo- derate-nzed private family they are made large enough to roafl a joint of meat and a couple of fowls at the fame time. It ihould be fitted up on one fide of the fireplace ; and a boiler, or, if it is neceffary, two, on the other fide, with their it earn- ers for vegetables, and an opening or two for fauce- pans and itewpans. The firegrate in the middle, being only intended to warm the apartment, need COMBUSTION. 67 be but a very fmall one* And the whole appear, ance of a kitchen thus fitted up is very neat, and much more comfortable, as a dwelling apartment for the fervants, never being overheated, .and the chimney never fmoking* ESSAY VII. THE DIFFERENT SOURCES OF HEAT. Besides the combuftion of inflammable fub- fiances, we have other means of exciting heat, , The friftion of two hard bodies, one againft the other, excites heat fufficient to fet fire to combufli- bles. Xnftances have occurred of forefls being burned down, in confequence of the wind produc- ing fuch conficlerable friftion between their boughs, as co fet fire to them. In the whale fifhery the precaution is neceffary, of wetting the line, and the part of the boat, that it is drawn over, as foon as the whale ftruck with the harpoon dives, and carries with it the vafl length of the line. Otherwife the friftion of the line drawn with fuch velocity over the edge of the boat, would unavoidably fet it on fire. Carriages by the fric- tion of the wheel upon the axle, mills, and other machines by friction of their different parts, have frequently been fet on fire, and deftroyed* In the iflands of the South Sea, in Africa, and in America, the natives have various means of ex- citing heat by friftion, to light iheir fires. Some rub fiat pieces of wood together. Others fit the end of a ftick, previoufly charred, in a hole made DIFFERENT SOURCES OF HEAT. 69 in a piece of wood, that is fattened to the ground, and then twirl the Hick with celerity till it inflames. Tinder is fometimes put into the hole, or brimftone rubbed on the flick to make it take fire more readily. Heat is likewife excited by concuflion. Iron by repeated blows with a hammer may be made hot enough to fet fire to inflammable fubflances, as is ufually praftifed by blackfmiths. By collifton we excite heat, when we Arike a light with flint and fteel. A fmall part of the fteel is detached, which is fo much heated, as to be fufed, and fufficiently fo, to inflame the tinder. The heat emitted by a change in the chymical compofit.on of a body, accompanied by a diminu- tion in its capacity lor heat, has been already noti- ced in fome inflances. Indeed combuftion is a change of this kind ; but there are fome other in- ftances worth mentioning, and particularly fome examples of fpontaneous inflammation. Inflammation has been known to take place from linfeed oil getting accidentally amongft hemp, or hempen cloth, which has been confumed in confe- quence. Some particular chymical change was here e Hefted, accompanied with a change of capa- city for heat, in confequence of which fo much heat was extricated, as to fet fire to the materials. The fame has happened with wool, and with lamp- black, when mixed with linfeed oil. 70 DIFFERENT SOURCES OF HEAT. When aqua fortis is poured upon any of the vo- latile oils, particularly if it has been previoufly mixed with one fifth of vitriolic or fulphuric acid, the mixture burfls out with a violent flame ; owing to the fame caufe, viz, a diminution in the capacity of the fubftances for heat. During every kind of fermentation, heat is evol- ved; thus, when green undried vegetable fubftances are heaped together, they begin to ferment, and of- ten emit fo much heat, as to take fire, as in hay- flacks made up before the hay is fufficiently dry. There are certain chymical compofitions, that poffefs this property of fpontaneous inflammation, and they are for this reafon called pyrophofi. The pyrophorus of Homberg which inftantly takes fire, when expofed to the air, is thus prepared. Melt equal parts of powdered alum and brown fug'ar over a fire, and keep ftirring them, till redu- ced to drynefs. Then introduce the mixture into a common phial coated with clay, and to which a glafs tube, open at each end, is luted. Keep the phial in a red heat furrounded with faiid, till no more gas efcapes by the tube; then clofe the tube with a little moift clay, to prevent the accefs of the air, and remove the phial from the fire. The gas that iffues from the tube may be inflamed by hold- ing to it a piece of lighted paper, and when the flame difappears, the operation is known to be completed. DIFFERENT SOURCES OF HEAT. 71 A pyrophorus is faid to be immediately formed, by rubbing together in a mortar fifty-four grains of fulphur, thirty-fix of very dry willow charcoal, and three of phofphorus. W e fhall now conclude the fubjedl of heat by 6b- ferving, that the term is often ufed to fignify a fen- fation, of which the pre fence of caloric, or matter of heat, is the caufe. Many are apt to imagine that this fenfation is a fufficiently accurate t eft of the temperature, or degree of heat of the air, and other bodies. Hence nothing is more common than to obferve, that this is very hot ; or that very cold ; that this is warmer than that ; or that the air is colder to day, than it was yefterday; whereas we only mean to fay, that to 6ur fenfatior.s, or feeling, fuch and fuch is the cafe ; but how for this is from accuracy in mo ft cafes, will appear from the fol- lowing obfervations. It frequently happens, that one perfon complains of the coldnefs of the air, at a time, when another is observing that it is warm, which is owing to their fenfes being differently affefted. But the fame per- fon too feels very differently at different times. If he comes out of a cold fharp air into a moderately warm room, he feels it fufficiently warm and com- fortable ; but when he comes out of a If ill hotter room into the fame apartment, he complains much of the coldnefs of it. This proves the inaccuracy with which we judge of heat by our fenfations; and 72 © IFFERFNT SOURCES OF HEAT. you may fatisfy yourfelf of the fame point by the following experiment. Put your right hand into a bafm of r water, as hot as you can well bear it, at the fame time put your left into very cold water, and after a few minutes take out both hands, and inflantly immerfe them into water moderately warm, and the right will feel cold, whilll the left feels warm. IS ESSAY VIII. OF LIGHT IN PARTICULAR. The confidefation of the laws of light, as to its refrangibility, its reflefiion, &c. belongs to the na- tural philofopher. W e have only to confider it as a chymical agent, /. e. to notice its influence on other bodies, fo far as its pre fence or ab fence regu- lates their chymical changes. We have already confidered it as bearing certain relations to heat ; we have alfo noticed its extrication, either from the- air, or from the inflammable body during combuf- tion ; and we fliali in a future Efiay find a more ap- propriate place, for explaining the phenomena of its emiffion from phofphorus, and certain bodies called phofphorefcent. We fliali therefore find but few circumftances to attraft our attention in this place; but it is of confequence both to the chymift, and the manufacturer, to be aware, that the prefence or ab fence of light is of more moment in a variety of operations, than it is generally conceived to be. Nitric acid, when expofed to the fun’s light, un- dergoes a gradual change, that 'would not take place if tlje light- were wholly excluded from it. It firlt becomes of a ft raw colour, and then pafles to a deep orange, and its other properties are at the fame time E 74 * OF LIGHT IN PARTICULAR* altered. The light is'fuppofed to unite with the oxygen of the acid ; for the coloured liquor cer- tainly contains a lcfs proportion of that acidifying principle, and oxygen gas is extricated from it dur- ing the aftion of the fun's light. This points out the necellity of keeping nitric acid, or aqua fortis, in painted bottles, or otherwise fecluded from the light. Kept in this manner it undergoes no changes, but without this precaution it acquires other properties, by which both the chy- mift and the manufa&urer, particularly the dyer, xnay in feme cafes be di Appointed. Very many coloured bodies are faded, or other- wife changed in colour, by long continued expofure to the light. This can only be in confequence of its effefting fome chymical change in the colouring matter, whether it be an artificial dye or the natural colour of the fubflance. The druggiff, aware of this, fhould keep his digitalis, or fox-glove, and other green vegetable powders, in bottles painted black, as the belt means of preferving their colour, and probably their medicinal virtues ; for there is great reafon to believe, that the fame chymical change that affe&s their colour diminiihes their vir- tues as medicines. That the fading of colours by expofure to the fun’s light is a chymical effeft, produced by the light upon the colouring matter, appears evident from its affe6ting differently articles dyed with OF LIGHT IN PARTICULAR. 75 different fubftances, though of the fame colour \ thus yarn, or other woollen goods, dyed red with kermes, retains its colour longer, and is lefs laded, than the fame dyed red with cochineal. It is alfo well known that one painter’s colours Hand much better than another’s, in confequence of their being differently prepared. The operation of light in effefting the fading of colours has been but little attended to; and the particular chymical changes which occur, are but imperfe&ly underflood. In many inftances it pro- bably depends upon the attratlion or affinity that exifts between light and oxygen. The blue colour of indigo depends upon the pre- fence of oxygen, for the colourlefs liquor obtained from the plants becomes blue on expofure to oxygen gas, and the gas is at the fame time abforbed. This being the cafe, fluffs dyed blue with indigo will be faded, or lofe their colour, by the abftraftion of oxygen ; and, as fight has fo flrong an affinity for that fubftance as to decompofe nitric acid, it is pro- bable that it alfo abflrafts it from indigo, and thus diminifhes and ultimately deflroys its colour. Stuffs dyed green acquire a yellowifh tinge by ex* p of are to the fight ; the deftru&ion of the blue colour by the above means will account for this, for green is a compound of blue and yellow. Purple fluffs in the fame way become readifh, that colour being compounded of blue and red. E 2 70 OF LIGHT IN PARTICULAR. In attending to the phenomena of vegetation it is found, that the prefence of light is abfolutely necefiary to the health of plants. If it is wholly excluded from them they foon become pale and fickiy ; they lofe the whole of their green co- lour, grow weak, wither, and die. Vegetables are blanched by the partial exclufion of light ; celery, by earthing it up round the roots, and cabbages or lettuces by tying their leaves together. The parts thus kept from the influence of the light, become pale and almoft colourlefs, and are then faid to be blanched. Plants that grow naturally in dark fituations are ufually of a pale colour; as the orobanche ramofa, which always grows under the fhade of hemp, the lathraea and others, that are found in the fhady parts of woods, and a variety of lichens growing upon trees. If light is admitted only into one part of the room, in which plants grow, they always incline towards that part; nature’s laws being in this inftance, as in others, fo wifely eftablifhed, and fo connefled with each other, that where benefit is to be derived from it, the effects of one lead to the completion of another. This inclination of the planf towards the light bears fo much the appearance of voluntary motion, regulated by a knowledge of the beneficial influence of light, that foine philofophers have brought it as 6 OF LIGHT IN PARTICULAR. 77 a proof that vegetables are endowed with reasoning faculties But how flight, how futile are their argu- ments, how falfe and unphilofophical their deduc- tions ; to aflame a new power, a reafoning faculty in plants, merely becaufe the confined and imperfect knowledge of man is unable to explain an aiceitained faft! How many thoufands of phenomena are our weak intellects unable to comprehend ! and how many of nature’s laws remain yet to be explored ! Would it not then be Ids prefumptuous to acknow- ledge our ignorance ; or more reafonable, to in- veftigate the nature of the faflt, than raflily to attri- bute to the vegetable world a faculty that we have no grounds for fuppofing it to poffefs ? The prefence of light we find to be neceflary to healthy vegetation. Its chymical effefls are fuch as to preferve and keep up thofe changes in the various parts of the plant that conftitute health. But this is not all ; the Creator of the world, the eftabliflier of all nature’s laws,, anticipating as it were the acci- • dental wants of individual plants, has fo ordained it, that the effe&s of light fhall alfo be fuch as to incline the plant, that is but partially expofed to it, towards the light, in confequence of which it re- ceives more and more of its genial influence. This is a beautiful infiance of the omnifcience and the beneficence of the Creator; and the philosopher viewing it in this light muff notice it with adraira- E 3 *8 OJ LIGHT IN PARTICULAR, lion, and acknowledge that infinite wifdom is appa- rent in the minuted ox his works. We confefs ourfelves ignorant of the means by which light has this particular effefi, as we avow ourfelves ignorant of the, means by which it influences th« colours of vegetables ; or by which any other at prefent inexplicable fa ft is accomplifh- .ed ; but fuch may become explicable to future chymids, and we ought to engage in the invediga- tion, rather than retard it by the affumption of a new principle. This hypothetical mode of reafoning puts a flop to inquiry by perfuading us, that we have explained fafts, when we have only exprefied them in other, and thofe more obfcure terms. Befides the effeft that light has upon the colour of vegetables, it is only during the influence of the fun's rays that they emit oxygen gas, or pure air. In the day time mod plants givdfout this gas in abundance, by which means the parity of the air is preferved, and a frefh fupply of its pure falubrious part afforded, in lieu of that which is dedroyed, or, to fpeak more properly, abdrafted hourly from the atmofphere by combudion, refpiration, and a variety of other proceffes. The prefence of light has confiderable effefts both in the procefs of bleaching, and in that of tanning. Cloth, expofed in the bleach-field, is whitened more rapidly in the day time than during the night, OF LIGHT IN PARTICULAR. T9 and more fo in a funny day than in cloud}' weather. In tanning, the procefs of handling the hides has more effeft, if performed in an expo fed, fituation, and whiHl the fun mines, than otherwife. Phofphorus, and fuch other fubftances, as emit light by a fimilar procefs, which is not dependent on a previous expofure to the fun’s rays, will be fpoken of in another part of thefe Effays. But there are certain fubftances, that feem, when ex- po fed to light, to abforb it, and afterwards gradually to part with it again, fo that when taken into the dark, they become luminous. Moft bodies po fiefs this property more or lefs, but fome more remarkably fo, than others. A mixture of fulphur and lime forms Canton’s phofphorus, and that of fulphur and an earth called barytes, the Bolognian phofphorus ; but thefe fub- ftances differ widely from phofphorus, ftriftly fo called. To make the former, mix equal parts of pul- verifed oyfter (hells and fulphur, and keep the mix- ture in a covered crucible, for an hour or two in a ftrong heat. If this powder is expofed to the light, and then taken into a darkened room, it appears luminous, and continues fo for a confiderable time* When it ceafes to emit light, this property is re- gained by its being again expofed to the light. Of other fubftances, that polfefs this kind of phof- j>horefcency, a better inftance cannot be brought, E 4 80 OF LIGHT IN PARTICULAR. than that df white paper. If you fhut yourfelf up in a darkened room, and contrive the means of ex- pofing a fheet of writing paper to the fun’s rays on the outfide, and then drawing it into the room, you will perceive the paper, when firfi drawn in, to be very luminous. It gradually becomes lefs and lefs bright, until it emits no light at all ; but you may again reftore its brightnefs by again expofing it to the light. Even the hand, when firfi Withdrawn from fun- fhine into a darkened room, emits light in the fame manner. The light thus emitted is in many infiances in* creafed by heat ; thus if a warm heater, fuch as is ufed in ironing, is drawn backwards and forwards over the (beet of writing paper, alter it is drawn into the darkened room, the paper is rendered more lumi- nous, and is made to give out light tor a longer time. Moreover, when it no longer emits light, its. brightnefs may in fome meafure be renewed by the heater, without again expofing it to the light. Sulphate of barytes or heavy fpar, and the fluate of lime or fluor fpar, only emit light when heated. Other fubftances are made to emit light by attri- tion, as when you break a lump of fugar in the dark, or fcrape with a knife pieces of pholphorated limeftone. It is interefting and ufeful to be made acquainted with thele fa£is, although v. e mult at 81 OF LIGHT IN PARTICULAR. prefent acknowledge our ignorance refpedling the caufe of them. Every one knows that light is emitted during the paffage of the eledlric fluid from one body to another. This in its paflage from one cloud to another, from a cloud to the earth, or from the earth to a cloud, conllitutes lightning. With an eledlrical machine many very amufing experiments may be performed, by exhibiting the light in a variety of ways ; but the confideration of this belongs to the natural philo- fopher, not to The chymifL When the back of a cat is ftroked by the hand in the dark, fmall Hallies of light or fparks are emitted, and at the fame time a crackling noife is heard. This is an eledtrica] phaenomenon. In the night time flalhes of light are fometimes obferved to be given out by certain flowers, par- ticularly thofe of the marigold. Many attribute this alfo to the eledlric fluid, but in forne cafes it pro- bably occurs from the difengagement of a phof~ phoric gas. 82 ESSAY IX. THE GASSES. OXYGEN GAS, OR PURE AIR. The Ample Jubilances or elements, that come next in order to be confidered after heat and light, are oxygen, azote, and hydrogen. They are never found alone or uncombined either in a folid or fluid Hate; but chymically united to fo much heat as to give them a gazeous form, they conflitute the Am- ple gaffes. In this ftate we fhall treat of them, but Ihall firft premife a few obfervations on gaffes in general. What chymifls have now agreed to call gaffes, differ from vapour, in being permanently aeri- form in every degree of temperature. No degree of cold is able to condenfe them into fluids or folids. Water is raifed in the form of vapour by heat, and is again reduced to the ftate of water by the abflrac- tion of its heat. Sulphur or brimftone is converted into vapour, when heated, and this vapour is con- denfed into a folid form by cold* or by abftra£tion of heat. But the common air of the atmofphere, in which we live and breathe, is not reducible to a fluid OXYGEN <5 A SV- 63 or folid ft ate by any degree of cold, be It ever fo in- tenfe; it is therefore a gas. All gaffes are invifible, but {fill we cannot doubt of their exigence, for we can retain them in proper veffels, pour them from one to another, feparate, or combine them at pleafure, and afeertain the parti- cular properties of each. Every thing, which in common language we call empty, is full of air or gas, and the method we employ, for pouring it from one veffel into another, is this : invert the jar. for in-fiance, which contains the gas, in a tub ol water with its mouth under the furface of the water ; fill the jar which is to receive the gas with water, and invert it in the fame tub ; then incline the firft jar, fo that its mouth fhall be under that of the fecond, and the gas will immediately afeend in bubbles to the top, and the water will rufh in the fame proportion into the firfi jar, till all the gas has left it, and puffed into the other. Though all gaffes are invifible, they are eafily proved to be different ; and each to poffefs its dif- tinft properties. A lighted candle hnmerfed into ajar of one kind of gas will burn in the ufual way, in another it burns with a much more brilliant flame* and in a third it is immediately extinguilhed. Thefe different properties will be difc'uffed, in treating of the different gaffes feparately; but at prefent only the fimple gaffes, namely, the oxy- E 6 84 OXYGEN GASf genous, the azotic, and hydrogenous, will be treated of; the compound ones, as carbonic acid gas, and others, will be confidered under the head of the fimple fubltances, to which they owe their chief properties. Oxygen Gas. Take a fmall apothecary’s phial, into which put an ounce or two of manganefe, and pour thereon a. fufficient quantity of fulphuric acid, to form a liquid pafle. Afterwards fit a cork to the mouth of the phial, with a hole through it, into which infert a recurved tube, with one of -its extremities entering the bottle, while the other is placed under the mouth of ajar, or phial, filled with water, and inverted in a tub of the fame. The tub (hould be furnifhed with a Ihelf, with holes in it, upon which the phial may reft in its inverted pofition. When the apparatus is thus difpofed, apply the heat of a lamp to the phial containing the manganefe, and a gas will immediately be difengaged, which is called oxygen gas, or vital air. It derives the firft name from its property of converting a variety of fubftances into acids, when combined with them, and from its being indeed the acidifying principle of all acids. It is called vital air, becaufe its prefence is abfolutely necef- fary to fupport the life of animals. Befide thefe two properties, it has that of fupporting and being neceftary to combuftioiit OXYGEN GAS* , 8^, Thefe three are the diftinguifhing properties of oxygen gas, and are poffeffed by no other fimple gas. Common air has the fame, only in confe- quence of its containing oxygen ; and in propor- tion as it contains more, it fupports animal life and comb u ft ion in a greater degree * The acids and their compounds will fall natu- rally to be confidered, when treating of the bafe of each acid. There is one however of the mi- neral acids, which has not hitherto been fatisfac- torily decompofed, and of which the bafe confe- quently is not known. This is the muriatic or marine acid,, or, as it was formerly called, fpirit of fait. As there is every reafon to believe, that it is a compound, and that oxygen is in this, as well as in all the other acids, the acidifying prin- ciple, we cannot treat of it with mo2e propriety in any part of the work, than in this. The muriatic acid is procured from common fait, by diftilling it with fulphuric or vitriolic acid. It comes over in the form of fumes, which are collefted and condenfed. This acid, further oxy- genated, is employed, either alone under the name of oxygenated muriatic acid, or combined with potafh, when it is called oxymuriate of potafh, in the improved method of bleaching, which has been of late fo advantageoufly adopted. The oxygenated acid is procured, when three parts of the acid, and one of a mineral called OXYGEN" CAS. 8G manganefe, are heated together; and if the va- pours are received in*o a folution of potafli, the oxymuriate is produced. The fame acid is like- wife obtained by pouring twelve parts of vitriolic acid, previoufly mixed with an equal quantity of water, upon a mixture of fixteen parts of com- mon fait with fix of manganefe. The vapours in this procefs may likewife be received into a folution of pctalh. The acid is thought fittefl for the bleaching of muflins, and the neutral fait is more generally em- ployed lor other goods. For whitening raw- filk, a mixture of twelve ounces of the acid with forty -eight pounds of fpirits of wine is preferred. In bleaching with this acid, it is ufed confiderably diluted, and the goods are previoufly boiled in a folution of potafh. Being then ileeped in the acid, they are afterwards waflied in clear water; and the fame procefs is repeated as often as it is found ne- ceffary. Common fait , from which muriatic acid is pro- cured, is a compound of this acid with the foffil alkali. It is found in three filiations; in large beds in the bowels of the earth, when it is called rock fait; in fprings of water which derive their fource in or near thefe beds, when it is called fpring fait; or in the water of the fea, when it is called fea fait. OXYGEN GAS* 87 The rock fait is feldom ufed, till it has been dillolved in water, and (Separated again by evapo- ration. Brine may be evaporated, either by expofure to the fun’s rays, or by artificial heat. In warm countries, the former method is adopted ; where, by receiving the fea water into proper refervoirs, that are made extenfive and (hallow, the fait is left covering the bottom of the pits, after the wa- ter has been evaporated by the heat. Salt, thus procured, is called bay fait. In our climate the heat is infufficient, and the rains too frequent, to allow of this plan being adopted with advantage; our fait is therefore procured by boiling the brine, and is of different degrees of purity, according to the heat, and as it is depofited in the latter or early part of the procefs. The aies oi common fait as a condiment, and as a preservative of meat, are lufficienily well known* bi t it is not fo generally underftood, that in fmall quantities,, inftead of retarding, it promotes putre- faction, which is the cafe. Salt is a uieful condiment to cattle as well as man. In tome parts of Africa large herds of ani- mals travel at Itated feafens to the coafi, where the fall plants abound. The fattening quality of our own felt marches is well known to glaziers. And in many countries it is the cullom to give felt with the food to moft kinds of cattle* O XT GEN GAS. When a candle or a piece of burning charcoal is introduced into oxygen gas, it burns much more* rapidly than in common air, and the charcoal emits beautifully bright fparks. If an iron wire twifted fpirally, and having a fmall piece of burning phofphorus, or fulphur, at the extremity, be introduced into a jar of this gas, the iron itfelf will be burnt, emitting fparks, and bright corrufcations, during its combuflion. By direfting a ftream of this gas through a blow- pipe to the flame of a candle, or any other com- buftible body, that is ignited, the mofl intenfe heat may be produced, that art has been able to effeft.- Metals and earths may thus be fufed that refill all' ether means. During combuflion in oxygenous gas the volume of the gas is decreafed, and, if the combuflion be con- tinued long enough, the gas wholly difappears. A union has taken place between the oxygen and the combuflible body, and the refult in many cafes is an acid. Thus, if fulphur is burnt, fulphuric or vitri- olic acid refults ; if phofphorus, phofphoric acid; and if carbon, or charcoal, carbonic acid. When combuflion takes place in common air, the fame phamomena occur, but lefs rapidly, and to a lefs extent. If phofphorus- be burnt in a jar of common air, inverted over water, part of the air is abforbed, which is fhown by the water rifing in the jar; and the phofphorus is, part of it,, con- COMMON AIR. S9 verted into phofphoric acid, which proves that it is oxygen that is ab forbed. The air that now remains* which is -jVoths of the whole, is no longer capable of maintaining combuftion, or life ; a candle put into it would be extinguiflied, and a moufe or any (mail animal would foon periflh. From this cir- curnflance it is . called azotic gas, or impure air, which is thus proved to be the other conftituent part of common air. Common air then is a compound of oxygen gas and azotic gas in the proportion generally of £7 parts of the former to 7 3 of the latter. The g and ufes of the air are well known to be, to maintain life and combuftion ; and as its pure part is thereby ablhra&ed, a continual fupply becomes neceffary, where thofe proceffes are carried on. That a continual fupply of air is neceffary to fupport life by refpiration, is made evident by ani- mals dying in an exhaufted receiver, and living, only for a given time in a given quantity of air ; a longer time the larger the quantity. A moufe, for inftance, confined in a jar of common air, the mouth of the jar being clofed, would presently be- come uneafy, \Vould gafp for breath, become con- yulfed, and, if allowed to remain in this filiation, would foon die ; but if frefh aii: be in time admitted to the jar, the moufe would revive. This (hows us, how important it is to renew the JVefh air of the rooms we live in a and to admit a COMMON AIR. SO fupply as faft as the pure part of it is abilrafted by- breathing, and by the burning of fires and candles. Inflead oi doing this, it appears, as if we confpired all we could to flop every avenue to its ingrefs. We fhut the windows as clofe as poffible, and put lift round the doors ; but luckily for us, ail we can do to ftop its entrance, is ineffeftual. Such is the difpofition of the air to reflore its equilibrium, that where there is a fire, to heat the air, and convey it up the chimney, the external air prefTes w T ith fuch force, as to make its way through every crevice. We do, however, in many cafes fucceed fo far in preventing the accefs of frefh falubrious air, as to prove its baneful effefts, In our theatres and ball-rooms the vitiated air has fo little opportunity to efcape, and the frefh air fo little to enter, that in fome parts a candle will fcarcely burn ; and an op- preflive weight acrofs the chefl fpeaks plainly to our feelings, that we want a freer atmofphere. In the narrow ftreets and lanes of man u faft u ring and commercial towns, peftilential difeafcs are a!- moft always prevalent, and the inhabitants of thefe places carry in their fqualid countenances the marks of conftitutional illnefs. All this in a great meafure proceeds from the want of pure falubrious air. Our prifons and our poor-houfes are too fre- quently, from the fame caufe, the refidence of difeafe. Although much, I am happy to fay it, lias of late years been effefted towards remedying COMMON AIR. 91 thefe grievances, much ftill remains to be done ; and the improvements for ventilating apartments, and maintaining the purity of the air, will not, I hope, be confined to thefe or fimilar buildings. Not only our hofpitals, our prifons, and other public buildings, require ventilation, and airy fitu- atibns ; but our private houfes, and particularly thofe of the poor, demand the fame. The fite and plan of a town is of national importance, for .the health of its inhabitants mud be greatly influ- enced thereby. The proper ventilation of our apartments ought to be ftrongly inculcated by thofe, who are aware of its utility, that it may become more generally adopted ; and the ignorant fhould be informed of the belt modes of accompliflung it. Every window or cafement fhould be made to open, and that always at the top. Thefe fhould be opened when we leave the room ; and in warm and < moderate weather may be frequently opened for a (Short time whilft we are there, particularly if many perfons live in the fame apartment. Much good would accrue from attention to this circum- ftance in man u faff ories, where many perfons are breathing the fame air for feveral hours together. In every (Situation it is proper to let down the fafh, or open the window, of fleeping apartments before we leave them. In many rooms it will be requifitc to have a con- &2 COMMON AIR* Itant communication with the external air* by meanif of an opening in fome part of it near the floor* In this cafe, and, indeed in every cafe of ventilation, the vitiated air will have exit at the top, and the ffefh air will come in at the bottom ; for the air that we have breathed and vitiated being heated,, immediately afcends and occupies the top of the room ; whilft the frefli air, -being colder, and of courfe heavier, comes in at, and occupies the lower part of the room. That this is the cafe will appear evident by the common ‘experiment of holding a lighted candle in different parts of the door-way of a room heated by company. The flame is driven outwards when held near the top, but into the room, when the candle is held near the floor. When a window opens from above downwards there can be no inconvenience felt from fitting near it ; for no cold air, as is ufualfy imagined, enters by the window, as will appear by holding a candle near the opening. The way to prevent a current of cold air from the opening at the bottom of the room is, to have a fianting board, to direft it fome way upwards.. In rooms having a plafter partition, or any other double partition, perhaps the beft plan would be to make an external opening through the outer plafter near the ground, and an inner one near the deling, or at leali above the heads of perfons ia COMMON AIR. 95 the room, that they might fuffer no inconvenience from the cold air. That eombuftion, as well as refpiration, vitiates the air, and requires a continual fupply, is evident from a candle only burning a certain time, if con- fined in a clofe jar, and by the fame continuing to burn a longer time if frelh air be admitted to the jar. This makes the ventilation of rooms ftill more neceflary, where there are candles and fires burn- ing; and it is, in my opinion, a great objeftion to our mode of warming apartments by open fires. If warmed by ftoves, the alh-pits of which are without, the air in the rooms would not be vitiated by the eombuftion; lefs cold air would be required, and, consequently, our rooms would be both warmer and more wholefome. Befides this, all parts of the apartment would be nearly equally warm, and we ftiould not experience the cold draughts of air that often ftarve us behind, whilft we are in other parts almoft burnt by fitting near the fire; which irregular warmth proves the caufe of rheumatifm, chilblains, and a variety of ailments. Befides the ufes of common air, which we have enumerated, it anfwers a variety of other important purpofes. The oxygen is abforbed from it in the calcination of metals. It is neceflary in moll cafes of fermentation. By the expaufion of air when 94 * COMMON AIR# heated, it becomes an eafy means of trail fmitting, or communicating heat, and thus preferves its equi- librium, or an equal temperature ; and, laftly, by its power of diffolving water, and holding in folu- iion more or lefs according to its temperature, it becomes the immediate caufe of fpontaneous eva- poration, and of dews, fogs, rains, and fnnilar phenomena. There is conflantly going on an evaporation of water, to a very great extent, from the fe^s, lakes, rivers, and from the whole furface of the earth, wherever there is moifture. The fea, it has been found by calculation, lofes many millions of tons daily by this procefs ; which lofs is fupplied by the rivers, that are conflantly flowing into it. The evaporation is increafed both by heat, and by the agitation of the air ; and therefore a warm and windy day is the beft for drying any thing ex- posed to the air. The wind affifts by removing the air, that becomes faturated with water, and thus admitting accefs to fuch as is not. It anfwers the fame purpofe as flirring does in promoting the rela- tion of fait in water. The heat aids the evaporation by increafing the folvent powers of the air, in the fame way that it promotes the folution oi fait in water, and enables it to difTolve a greater quantity. On this property, that air when heated is able to hold or retain more v/ater than when cold, depends the explanation of a variety of phenomena. Hot 9 COMMON AIR. 95 water will diiTolve more fait than cold water; there- fore hot water, that is faturated, will depofit part of the fait on cooling. In the fame way, and for the fame reafon, hot air, that is faturated with moifture, will depofit part of it in form of dew, rain, & c., when it becomes cold. During the day-time the fun’s rays having warm- ed the earth, and that portion of air that is near its furface, this ftratum of air is enabled to hold a good deal of water in folution. But when the fun fets, the earth and adjoining ftratum of air are fo much cooled, that the latter is unable to hold all the water, which it had formerly diffolved, and the con- fequence is a depofition of it in the form of dew . Dews are feldom feen more than a very few feet above the ground, becaufe the ftratum of air cooled by the abfence of the fun extends no higher. Pictet has afcertained by experiment, that the air is colder near the furface than fome feet above it during the night, and warmer during the day. In the morning, when the fun has warmed the earth, and lower ftratum of air, fufficiently to enable this to diflolve all the moifture, that it now contains, there is no longer any depofition, and confequently no more dew. Dews are mo ft frequent, and mod abundant, when there is the greateft difference between the temperature of the air in the night, and that in the 96 COMMON AIR* day, as in the autumn, when very cold evening! fuceeed to very warm days. A haze, mifl, or fog, is a fimilar depofition from a larger body of air, extending to a greater height. The caufe of this depofition is fuppofed to be the paffage of a colder or a warmer Hream over one that is of a different temperature, or the meeting of two ftreams not equally heated ; in which cafe the mix- ture is unable to hold all the water in folution, that they held when feparate. In clouds the water is probably in the fame flate ; s in mills, but the warmth of the inferior' firata pre- vent its falling below a certain point. When two clouds meet that are of different tem- peratures, or. in different Hates of eleftricity, I con- ceive that a further depofition enfues ; and that ac~ cording to the temperature, and the fuddennefs of the depofition, the water affumes the form of rain, fnow, or hail. Sauffure fuppofes that water exifls in three dif- ferent Hates in the atmofphere ; firft, in a Hate of vapour, that is invifible, as when evaporated from moifl bodies ; fecondly, in a veficular form, as in clouds, where it exifls in frnall bladders or vefictes; and, thirdly, in a true aqueous form, as in rain. He fuppofes that in thefe three Hates its capacity for heat is different ; that the vapour has a greater capacity than the veficular Hate, and the veficular greater than the aqueous Hate. COMMON AIR. According to this fuppofition there will be an evolution of heat when vapour is converted into dews, fogs, and clouds ; and again when the latter are converted into rain, fnow, or hail. According- ly, it is frequently obferved, that a fhower in cold weather, or a fall of fnow, warms the air. And it may be added, that Pi£let obferved his thermometer, at the top of a pole 75 feet high, to rife between one and two degrees, when furrounded with a fog. By the various means, which we have now men- tioned, all the water that is evaporated, and taken up by the air, is again dcpofited in raiir, and dews, to fupport the life both of the animal and vegetable world. It is then carried by the ftreams and rivers to the ocean, to be again evaporated, and anfwer again thefe beneficial purpofes. When a glafs of cold water is brought into a warm room, or a bottle of wine out of a cold cellar, a dew is immediately depofited on the outfide; this is becaufe the warm air in contact with the glafs is fuddenly cooled, and thereby rendered incapable ; of retaining all the moifture which it had previoufly diffolved. In a warm room, where there are many people, and confequently much moifture for the air to ab- forb, a dew is depofited on the infide of the win- dows ; becaufe the cold external air cools, through the medium of the glafs, that portion of the internal 99 COMMON AIR. air that is neareft to it, which of courfe depofits its moiflure. When the air in the room is colder than the ex- ternal air, a dew is depofited on the outfide of the window. In winter time the dew depofited on the infide •f the windows is frozen, afTuming very grotefquc appearances, as obferved in a frofly morning. 99 ESSAY X. AZOTIC GAS, OR IMPURE AIR. Azotic gas exifls in great proportion in the at- mofphere ; being, as we have already faid, one of its conftituent parts. Whenever we abftra£l the oxygenous gas from common air, the residue is azo- tic gas. If therefore we burn a candle or any other combuftible body in a jar containing common air, the remaining air after comb union is azotic gas or impure air ; and if the ccmbu&iole body is phof- rus, the gas is tolerably free from any admixture. A candle immerfed in this gas in Handy goes o t ; and if an animal is confined in k, it foon dies. Its prefence in the atmofphere feems to temper and moderate the aftion of the oxygen; far without it combuftion would be too violent and rapid, and the oxygen breathed alone would excite inflammatory complaints and foon prove fatal. Azotic gas is emitted during animal putrefaction. It is given out by ripe fruit, and by flowers ; hence the impropriety of keeping either in apartments where we live. The air is confiderably vitiated by keeping pots of flowers in clofe rooms, as in bed- chambers ; and bad effeCts have frequently pro- ceeded from it. Mufhrooms are obferved to evolve F 2 100 AZOTIC GAS, OR IMPURE AIR. this gas, whilft growing, and to afford more when chyinically analyzed than other vegetables ; they approach in this refpect to the compofition of ani- mal matter. It is a fubjeft, that requires further chymical in- Veftigation, to afcertain the particular changes, that are effefted during the putrefaQion of animal mat- ter. We might be enabled by it to difcover better means, than are now known, to preferve meat ; and probably to recover it after the putrefa&ion has commenced. We know that the prefence of air is neceffary to putrefa£tion, and that warmth and moifture promote it ; we therefore prefer a cool and dry (ituation for our larders. Meat may be long preferved in veffels of fixed air, andmieans might, I think, be invented for making this an eafy prac- tice. Meat that is confiderably tainted, may be rendered more palatable, either by burying it for a few hours under ground, or by covering it with powdered charcoal. The meat of animals, that have been hunted, or otherwife violently exerci- fed, inclines very quickly to putretaftion, and is confequently tenderer than other meat kept the fame length of time. Animals killed by lightning, or by a ftrong electric fhock, which is the famethmg, have the fame difpofition to putrefy ; and the latter mode has been recommended for killing poultry, that is to be eaten immediately. AZOTIC GAS, OR IMPURE AIR. 101 The combination of azote and oxygen, befidcs affording common air, which we have already treated of, conftitutes a variety of other fub fiances, according to the proportions of the two ingredients. Nitric acid or aqua fortis is a compound of thefe two elements, and may be made by repeatedly paf- fmg e.leci.ric fhocks through a mixture of oxyge- nous and azotic gas. The analyfis of this acid proves the fame thing ; for when it is made to pafs through a red-hot porcelain tube, a mixture of oxygenous and azotic gas is obtained. The procefs ufed in manufacturing the aqua for- ti-s for commerce, confifts in mixing one part of faltpetre with two or three of red boiar earth. This mixture is put into coated retorts, difpofed in a gallery or long furnace, to each of which is adap- ted a receiver. The firfl vapour, that arifes in dif- tillation, is nothing but water, which is fuffered to efcape at the place of junfture, before the luting i$ applied ; that is, before the juncture is clofed up with a compofition of meal and water, or with gla- zier's putty, or fome other fubftance, called luting. When the red vapours begin to appear, the phlegm, which is condenfedin the receiver, is poured out, and the receiver being replaced is carefully luted to the neck of the retort. The vapours, which are con- denfed, form at firfl a greenifh liquor ; this colour difappears infenfibly, and it then becomes more or F * 102 AZOTIC GAS, OR IMPURE AIR. iefs yellow. This is the common aqua fortis, which requires purification for chemical purpofcs. It may alfo be oburiicd by ch {tilling the fu!p!:u- nc acid upon nitre or riuuUue. When pure, it is colourlefs. It is tried In dyriug, and in feveral proceffes by the manufacturers in metals, as in gild- ing, &c; In confeqrence of its diffolving metals it is ufed in etching upon copper. It is alfo a ufe- ful medicine in a variety of complaints. Nitric acid has a peculiar effeCt upon animal mat- ter, converting it into a fatty fubftance, very like fpermaceti. The fame converfion of animal mat- ter into an inflammable fubftance has been obferved to be effeCted by a natural procefs in certain fixa- tions. Touret, a French phyfician, has defcribed the .appearances met with on opening a vault in the bu- rial ground des Innocents. Many of the bodies, that had been buried a great number of years, were found to retain their form, and confiftence, and in many refpefts their natural appearance. When they were examined, it was afcertained, that moft parts of the body were converted into a fatty or rather fpermaceti-like fubftance that was inflammable, and burned like fpermaceti. Dead animals thrown into running ftreams have undergone a fimilar change in many of their parts, particularly the flefh or mufcular parts. And nitric acid poured upon a piece of flefh has been difeo- r AZOTIC CAS, OR IMPURE AIR. 103 rered to effeft the fame change. From thefe faffs there is little doubt, but that by proper management horfeflefh, and that of animals dying of difeafe, might be converted to the ufeful purpofe of making foap or candles. Saltpetre, from which aqua fortis is obtained, is a combination of this acid and potafh. It is pro- cured fometimes by natural proceffes, fometimes by artificial means. In fome countries the foil contains it, where they have only to colleCt what efflorefces on the furface ; wafh it well, boil the water, evaporate, and then cryflallize the fait. It is found in this ftate in the Indies, and alfo in fome parts of Spain. In general, however, it is formed artificially by colle&ing animal and vegetable fubftances into heaps, and fufFering them to putrefy. The animal matter affords azote, which attra&s oxygen during putrefa£lion, and thus forms nitric acid. The vege- table matter affords potafh, which uniting with the new formed acid conflitutes the nitre. In the North of Europe thefe faltpetre beds are formed with lime, alhes, earth of uncultivated grounds, and ftraw, watered with urine, dung-hill water, and mother waters *. Of animal matter, blood, and next urine, favour the production of faltpetre moll Of vegetable matter, light minutely-divided earth, in which plants * Ttefufe waters from various manufactures. F 4 104 AZOTIC GAS., OR IMPURE AIR* have grown and decayed fucceffively for ages, la fittefl to form thefe beds. From th£ artificial a^well as natural nitre-beds the fait is extra&ed by wafhirtg the earth in- water, evaporating, and then cryftallizing. Obtained by this firfh operation the fait is never pure, but contains common fait, and* an extraftive colouring principle, from which it muft be cleared* For this ptirpofe it is diffolved in frefh water, which is evaporated, and to which bullock’s blood may be added, to clarify the folution. The nitre obtained by this fecund procefs is termed, nitre of the jeoond i oiling. The purified nitre is employed in making the better fort of aqua fortis, and in the compofition of gunpowder. Saltpetre of the firll boiling is made ufe of in manufacturing an inferior aqua fortis for the ufe of dyers. We have faid, that faltpetre is an ingredient in gunpcivder. This powerful compofition is a mix- ture of feventy-five parts of faltpetre, nine and a half of fujphur, and fifteen and a half of charcoal. This mixture is triturated from ten to fifteen hours # ' in pounding-mills, having their peitles and mortars of wood, care being taken to moiflen it from time to time. It is then palled through fieves of fkin, and granulated. The powder is then fifted to fepa- rate the duft, and, laftly, carried to the drying houfe. % AZOTIC GAS, OR IMPURE AIR. 105 Cannon powder requires nothing further; but for fowling powder, the procefs of glazing is neceffary. This is done by putting it into a kind of cafk, which turns upon an axis, by the motion of which the angles of their grains are broken, and the furfaces polifhcd. In the compofition of gunpowder, it is not ne- ceffary to attend exactly to the proportions directed above ; for, although the proportion of faltpetre cannot be varied much without detriment, that of the other two ingredients rriav vary confiderably* without very materially altering the properties of the powder. The purity of the materials is of very confiderable confequence, and fo is the circumftance of their being very intimately mixed. If the falt- petre contains any portion of common fait r which* is ufually the cafe with the inferior forts, it injures the powder by attracting moiflure from the atmofo phere. Gunpowder moiftened by this caufe, or by any accident, lofes its power, in confequence of the water diffolVing the faltpetre, and feparating it from’ the other ingredients. When thus damaged, if by pure water, it only requires to be again powdered and regranulated ; but if fait water has caufed the damage, it cannot be remedied ; the ingredients* however, are valuable, for the faltpetre may eafipy Le feparated by foiution and cryflallization. The effl of gunpowder are owing to the iuddm formation of a quantity of gas, and are conlequertlyg F 5, 10G AZOTIC GAS, OR IMPURE AIR. greater when the gas is confined in all dire£lion§ but one, as in our guns and cannons. The nitric acid of faltpetre is decompofed, and affords the gas. The other ingredients difpofe it to be eafily inflamed, which is neccffary to the decompofition of the acid. A fulminating powder , pofTeffing far greater powers than gunpowder, is formed by mixing and triturat- ing three parts of nitre, two of fait of tartar, and one of fulphur. A few grains of this heated in an iron ladle over the fire is firft melted, then affords a blue flame, and at lafl: a violent explofion. When the nitric acid is poured upon iron, cop- per, or zinc filings, there is a confiderable difen- gagement of air, which affumes a red colour, but which, if collefted in a jar previoufly filled with water, and inverted in a tub of the fame, is colour- lefs, and is known by the name of nitrous gas. Nitrous gas is, like nitric acid, a compound of oxygen and azote ; but in this the proportion of oxygen is much fmaller. It will fupport neither combuftion nor animal life. When mixed with oxygen gas it unites and forms nitrous acid, which appears in red vapours. When mixed with common air the fame takes place, which is the caufe of the red vapours that appear when the nitric acid is poured upon the iron or copper filings. As the nitrous gas combines only with the oxy- genous or pure part of common air, it has been employed to afeertain the quantity of oxygenous - - . • i v . * v* % AZOTIC GAS, OR IMPURE AIR. 107 gas, and confequently the purity of the air. Ufed in this way, it is called a eudiometer . For this purpofe, a given quantity of nitrous gas is added to a certain quantity of common air, or any other, that is required to be examined. The mixture is made in a graduated tube over water, and in pro- portion to the quantity of oxygen the volume of air is diininilhed, and the water rifes in the tube. The height to which the water rifes is the meafure of the purity of the air. By expofmg nitrous gas for a few days to iron filings, it lofes part of its oxygen, and then con- fiitutes a gas called nitrous oxyd, which is confe- quently a compound of oxygenous and azotic gas with a lefs proportion of the former even than nitrous gas. Nitrous oxyd may be obtained by a variety of other means, but the pureft is got by the following procefs, as direfted by Mr. Henry. To diluted nitric acid add carbonate of ammonia (the common fmelling falts) till the acid is faturated. Then eva- porate the folution ; and to fupply the wafle of alkali, add occafionally a little mor. of the carbonate. Let the folution be evaporated by a very gentle heat to drynefs. The fait thus obtained is next to be put into a glafs retort, and diddled with, a fand heat, not exceeding 500° Fahrenheit. The heat of an Argand’s lamp even is fufRcient.. The gas may he colletled over water, and allowed to ftand a few F 6 108 AZOTIC GAS, OR IMPURE AIR. hours before it is ufed ; during which time it will depofit a white cloud, and will become perfeftly tranlparent. The great peculiarity of this gas is, that it fup- ports combuftion, and not the life of animals. Molt inflammable bodies, as charcoal, fulphur, phofphorus, and even iron wire, burn in this gas with nearly as much rapidity and fplendour as in oxygen gas. The nitrous oxyd is decompofed, and its oxygen unites to the inflammable body. When an animal is wholly confined in this gas it fpeedily dies, but when breathed for a fhort time from a bladder or oiled-filk bag it has a very ex- traordinary effeft. We have very refpeftable tefti- monies to the peculiar fenfations it excites, in an eflay published on the fubjeft by Mr. Davy. Molt perfons exprefs their feelings on the occa- fion, as highly pleafurable. They experience great exhilaration, and feel an irrefiftible propenfity to laughter, as well as an unufual difpofition to muf- cular exertion. Their ideas are vivid, and flow 'rapidly; and, in Ihort, they experience what moll perfons do in the pleafant period of intoxication, without fuffering any of the unpleafant effefts that ufually fucceed intoxication. With the various compounds of oxygen and azote now defcribed, we finilh the confideration of thole dements, and pafs to that of hydrogen* 109 ESSAY XT. HYDROGEN GAS, OR INFLAMMABLE AIR. Hydrogen, as its name imports, is a conflitu- ent part, of water, of which oxygen is the ©ther ingredient. It is from the decompofition of water that we obtain hydrogen gas, and this is done in a variety of ways. We fhall defcribe only two 5 the firft of which is the moil eafily accomplifhed, and the latter is moil economical, which is of confequence, when a large fuppiy oi this gas ijr required. The fini mode only requires you to pour fulphuric acid, or oil of vitriol, previoufly diluted with five or fix times its weight of wa*er, upon iron filings, or fmall iron nails, in » phial or glafs retort with a recurved tube. An effervefcence will enfue, and the efcaping gas may be collefted in a jar under water. ' To obtain this gas in the large way, procure a gun-barrel, the breech of which has been removed, fo as to form a tube open at each end. Fill this with iron wire, coiled up in a fpiral form. To one end of the barrel adapt a fmall glafs retort, partly filled with water, and to the other a bent glals tube, the open end of which terminates in 110 HYDROGEN GAS, OR INFLAMMABLE AIR, the receiving vefTel. Let the barrel be placed horizontally (or rather with that end to which the retort is fixed a little elevated) in a furnace having two openings in its body oppofite to each other. Light a fire in the furnace; and, when the gun-barrel has become red hot, apply a lamp under the retort. The fleam of the water will pafs over the red hot iron, and will be decom- pofed. Its oxygen will unite with the iron, and its hydrogen will be obtained in the form of a gas. This gas burns with a filent lambent flame, when in contaft with common air; hence its name of in- flammable air. When previoufly mixed with common air, an explofion takes place on the ap- proach of a lighted match or candle. This gas of itfelf, however, extinguifhes a burning body ; thus, if ajar containing inflammable air is brought in an inverted Hate over the flame of a candle, and depreffed, it immediately extinguifhes it. Its other properties are, that animals confined in it foon die, though plants live and thrive in it, and that it is very considerably lighter than com- mon air. Knowing it to poffefs thefe properties, we Shall be able to explain many very curious fafts. Artificial fireworks are made by palling this gas through metallic tubes, varioufly difpofed, and furnifhed with a variety of orifices, through HYDROGEN GAS, OR INFLAMMABLE AIR. Ill which the gas can efcape. The machine, to which thefe complicated tubes are affixed, is made moveable wholly, or in part, and in different di- regions, fo as to add much to the effeft. The gas is inflamed at all thefe orifices, where it comes in contaft with the atmofpheric air, and burns with a ftill flame. A conltant ftream of it is fupplied by prcffing the bladders, or bags, that contain it, and that are connefted to the main tubes, from which all the others branch out. The mod common explanation of the aurora borealis, or northern lights, is, that a ftratum of hydrogenous gas above the atmofphere of com- mon air is lighted by the eleftric fpark, and burns (lowly, where it comes in contact with our com- mon air. The corrufcations of light obferved chiefly in northern latitudes are perhaps referable to the fame caufe. The levity of this gas, com- pared with that of common air, will account for its occupying a higher region ; and, as it can only burn, where it is in contafl: with the latter, the appearances we obferve in the aurora borealis are exactly fuch as we fhould expeft from fuch a caufe. Inflammable air or hydrogenous gas is frequently extricated in mines, probably from the decompo- fition of bituminous or coaly fubftances. It is -called by the miners fire-damp; and is to them a fource of great danger, as well as inconvenience; 115 IIYDRGGEN GAS, OR INFLAMMABLE AIR. for, by becoming mixed with the common air, it is fubjecl to fudden and violent explolions, when- ever a lighted candle or other ignited body is acci- dentally brought into contact with it. In flagnant muddy water, where the putrefac- tive procefs is conflantly going on, both of ani- mal and vegetable matter, there is a confiderable difengagement of inflammable air, which is feen riling to the top in bubbles. It is eafily colleQed by inverting a wide-southed jar, filled with water, in one of thefe flagnant pools, where the bubbles are obferved, and then ftirring up the mud from the bottom with a flick. This agitation caufes a more rapid difengagement of the gas. The gas thus procured is found to contain a con- fiderable portion of another gas, viz. the carbonic acid gas or fixed air. The evolution of thefe gaffes from fuch marfhy fituations is in con Sequence of the decompofition of water by the putrefying ani- mal and vegetable matter. The oxygen of the water uniting with the carbon of the putrefying mafs forms the fixed air, whilft the hydrogen of the water _efc apes in the form of hydrogen gas. It muff be remembered that the bubbles of air feen to arife from ffreams, and clearer water, in which the green conferva ai'd other vegetables* grow, as the duck-meat (lemna), or chick-weed (alfme or ftellaria media), is pure air or e> vge'nous gas, and not this inflammable air. 'HYDRO-GEN GAS* OR INFLAMMABLE AIR. 115 In confequence of this gas being fo much lighter than common air, it has been applied to the purpofe of forming air balloons. A bladder or bag, made of waxed canvas, or oil-fkin, when filled with this gas, is much lighter than the fame bulk of common air, and therefore rifes from the ground when liberated, as naturally, and by the fame law, as a cork p re fled down under water, rifes to the top when the force is removed. The larger. the balloon, the greater weight it is able to raife with it; but the higher it mounts, the lefs weight ijt is able to carry. The reafon of this latter circumftance is, that the higher it gets the rarer is the air, and confe- quently the lefs is the difference between the fpecifis gravity of the air in the balloon and the furround- ing air. On this depends the utility of carrying ballaft, when it is required to mount high in the air. TheYnore ballaft your balloon is able to raife, by being made large, the higher you may afeend; for by gradually throwing out the ballaft, you mount ftill higher in the air. When it is required to defeend, the inflammable air is fuffered gra-» dually to efcape from the balloon; by which means it becomes fpecifically heavier than the atmof- pheric air, and confequentiy falls gradually to the ground. The inconveniences experienced by aeronauts, when the balloon has reached the ground, i 14 HYDROGEN GAS, OR INFLAMMABLE AIR# in confequence of its rebounding, and often drag- ging the travellers to a confiderable diftance, might be obviated by contriving the means to let the whole of the gas efcape as foon as the balloon has touched the ground. Another kind of balloon is formed by filling the bag with heated air inftead of hydrogenous gas, and by keeping it in the fame heated ftate, which is done by means of a fire under the balloon, having a communication with its cavity. The air in the balloon in this cafe being rarefied, and made fpecifically lighter than the furrounding air, rifes and carries a weight with it upon the fame principle as the firft kind of balloon. An amufing experiment, proving the lightnefs of this gas, may be performed by forming foap bubbles with it inftead of common air. For this purpofe fill a bladder with the gas; if the bladder is furnifhed with a ftop-cock it will be more con- venient; and then adapt it to a common tobacco pipe. Dip the bowl of the pipe into a lather of foap, and by prefting the bladder blow it up into bubbles. Thefe bubbles, from their extreme levity, rife very rapidly. We have faid that hydrogen and oxygen form water; and, in the experiments detailed for pro- curing hydrogenous gas, we have proved it analy- tically; for whilft this gas comes over, the other HYDROGEN GAS, OR INFLAMMABLE AIR* 11* conftituent, oxygen, is united to the metal, that it employed. We have alfo fynthetical proofs of this compofh tion of water, one or two of which we {hall recite ; and thefe we trull will {office. When a mixture of hydrogenous and oxygenous gaffes is made to explode, there is always a formation of water; but in a fingle experiment it is too minute to be com- pletely fatisfaftory, although a dew may generally be obferved to be depofited on the Tides of the veffel in which the experiment is performed. By the flow but continued inflammation of hy- drogen gas in common air, a fufficient quantity of water may be formed to fatisfy any one with refpect to its compofition. This may be done in the fol- lowing way: fill a bladder, furnifhed with a flop- cock and pipe, with hydrogen gas. Procure a glafs globe, having two openings oppofite to each other; then fet fire to the ftream of hydrogen gas paffing from the tube, and introduce it into the centre of the globe. The combuftion may be con- tinued, if required, till all the inflammable air is burnt; and drops of water will be obferved running down the infide of the globe. The ele&rical piftol is a machine contrived for exploding a mixture of inflammable air and com- mon air by means of the eleftric fpark; and the force of explofion is made to drive out a cork, or other folid body, w T ith fome violence. 116 HYDROGEN GAS, OR INFLAMMABLE A I R> Each time that the piflol is fired, a minute quan- tity of water is formed; and if the experiment is frequently repeated with the fame piftol, its inter- nal furface becomes very fenfibly moiftened. In iron foundries, and in manufactories where otlier metals are melted, very feriou'fc accidents have happened from only fmall quantities of water getting accidentally into contact with the heated metal. If only a few drops of water happen to be in the eaft or mould, which is to receive the melted metal, a moll violent explofion is fure to enfue, as foon as the metal comes into contaft with it. The fluid metal is thrown about in every direftion, and the workmen of courfe are dreadfully burnt. The efleft here is much greater than it would be from the mere converfion of the water into vapour; and it is now afcertained, that it arifes from the decom- pofition of the water, and confequent formation of inflammable and pure air; a few drops of water affording a very large volume of the airs. It is unneceffary to fay any thing refpe&ing the important ufes to which water is applied. To pre- serve it fweet during long voyages, it is neceifary that the watercafks fhould be well charred on their infides. This is found to be the bell means of pre- venting the decompofition of the water, which is the caufe ol its becoming difagreeable to the tafte, and unwholefome. Many fuppofe that water be- comes tainted in confequence of the putrefa&ioja of HYDROGEN GAS, OR INFLAMMABLE AIR. 117 animalculae and fmall vegetables, which it contains; hut this is not fo much the caufe, as a real decom- pofition of part of the water, which is effe£ied by the juices and other parts oT the wood of the calk attrafting the oxygen of the water. The hydrogen remains in the water, and gives all the unpleafant properties to it. Charring of the calks is the bell preventive. Tainted water may be fomewhat re- covered by ftirring in it powdered charcoal. 118 ESSAY XIE CARBON, OP, CHARCOAL : CARBONIC ACID GAS, OR FIXED AIR, Carbon is the name given by chy mills to the pure part of charcoal. It is prefent in almoft all combuftible bodies, and is itfelf completely com- buftible. Carbon is not decompofable, and there- fore ranks amongft the chymical elements. The jnoft interelling compound, of which it forms the bafe, is its union with oxygen, when it forms the carbonic acid gas, or fixed air. This compound will furnifh us with materials for the prefent efiay ; but firft it may be as well to fay fomething of charcoal. Charcoal, as met with in commerce, is ob- tained from the partial combuftion of wood. Bil- lets of any kind of wood are heaped up into piles, ufually in the form of pyramids. The whole is then covered with earth, leaving an aperture at top and bottom for a current of air. The pile is now fet fire to, and when completely ignited throughout, the apertures are clofed, and the fire consequently fmothered. In this procefs all the juices of the vegetable, its oils, &c., are diffipated, leaving little more than its woody fibre. It lofes about three* CARBON, OR CHARCOAL, &C. 119 fourths of its weight, and what remains is called charcoal. This charcoal contains, befides carbon, fmall quantities of different kinds of earth, fome water, and, it is now fuppofed by fome, a proportion of oxygen. When charcoal is burnt, its carbon unites with the oxygen of the air, and fo much heat as to give it the gafeous form, and conftitutes carbonic acid gas, or fixed air. The fame gas is alfo obtained by the combuftion of the diamond, proving that this precious and coftly article is carboh or charcoal in a very indurated Hate, and affuming a determinate form. It was not till lately that the diamond was proved to be com- buflible ; but by means of the blow-pipe, and a flream of oxygen gas, it may be, to fpeak in com. mon language, wholly confumed. The air, that is extricated during the combuftion, is carbonic acid gas, proving the diamond to have been chiefly, if not wholly, compofed of carbon. Long before this fafl: refpe&ing the diamond was afcertained, Sir Ifaac Newton, reafoning from its great refrafting power, declared it to be his opinion, that it was one of the moft combuftible of bodies. Modern difcoveries have now proved the fa£i; and it affords us an admirable inftance of the acumen of that great philofopher. The carbonic ACID GAS, which we fha now t 1 20 CARBON, OR CHARCOAL: take into coilfi deration, may be obtained much purer by other means than by the combuftion of charcoal. It is this gas that is extricated in almofl all cafes of effervefcence, as when vinegar, or any other acid* is poured upon chalk, marble, lime- flone, or potafh. The beft way of procuring it for experiment is, to pour diluted ful ph uric acid upon chalk in a com- mon phial, furnifhed with a bent tube. The gas may then be received in jars over water. It poflefles the following properties: it is much heavier than common air : it extinguifhes flame, and is fatal to animals : it pofleffes the properties of an acid, and precipitates lime from lime water. By keeping in mind thefe properties, we lhall be able to deteft the prefence of this gas under a va- riety of circumftances, and thus be enabled to account for various interefting phenomena. We fhall find that it is extricated during the ferment- ation of beer, and other liquors ; that- it is formed during many inftances of combuftion, and by the refpiration of animals ; and, alfo, that it is met with naturally in certain mineral waters, and in many other fituations. Fermentation is the term ufed to fignify thofe changes that take place in dead animal and vege- table matter, when expofed to the aftion of the air, and kept at a certain temperature. If the faccharine or fugary principle predominates in the fubftances CARBONIC ACID GAS, OR FIXED AIR. 121 employed, the produft will be a fpirituous liquor, and the procefs is called the fpirituous or vinous fermentation. When a mucilaginous, or gummy matter abounds, vinegar is formed, and the procefs is then termed the acetous fermentation. Sub- fiances that have already undergone the fpirituous, will, very often, pafs to the acetous fermentation, particularly if kept warm, and at the fame time expofed to the air^ Lafily, when gluten or jelly exifts in confiderable quantity, as in animal matter, that kind of fermentation, termed putrefaffive, is fure to take place ; and the product here, that is cha- ra&eriftic of the kind of fermentation, is ammonia, or volatile alkali, fuch as the common fmelling falts. We fha!l in this place confine our attention to the vinous or fpirituous fermentation; during which there is evolved a very confiderable quantity of carbonic acid gas, or fixed air. This is the pro- cefs by which we obtain fpirits of all kinds, as rum, brandy, gin, &c., alfo every kind of wine, of cider, perry, or beer. In making any of thefc liquors, it is neceffary that a quantity of fpirit I fhould be formed, and the procefs is in all alike. Wine is made of the mutt or pure j uice of grapes, or of the juice of other fruits diluted with fugar and water in order to difpofe it to the vinous fermenta- tion. The mixture fhould be kept at a heat equal to about 70 ° of Fahrenheit : hence the advantage of making wines in warm weather. It now foon be. G 1-2 CARBON, OR charcoal: comes turbid, and air bubbles are feen to rife te the furface, which are the carbonic acid gas, or fixed air. This air being entangled in the pulpy part of the fruit, caufes part of it to rife to the furface, in the form called yeaft or barm. A fediment is at the fame time gradually depofited ; and as the bubbles of air at top burft, and let fall the pulpy part that it was entangled in, the wine is left clear and tranfparent, .fit for calking. That it is carbonic acid gas, that is thus extri- cated during the vinous fermentation, is proved., firft by holding a lighted candle, or piece of lighted paper, over the fermenting liquor, when it will be inftantly extinguifhed^ and next by half emptying a bottle of lime water in the fame fituation, and then fhaking the remainder, which will thereby become white and turbid. This gas., being much heavier than common air, always keeps its place over the furface of the liquor, till it rifes as high as the edge of the tub or vat, and then it defeends to the floor ; fo that, if you hold the candle only a few inches above the edge of the vat, it is not extinguifhed ; but goes out immediately when held over the liquor, and below the top of the vat. This is the reafon too why, when the vat is emptied of the liquor, the gas for fome time occupies the bottom of it, fo that it is unfafe for the workmen to get into it, with GARBON'IC ACID GAS, OR FIXED AIR. 12$ a yiew of cleaning it. This is well known to the labourers in breweries, who never defcend into the vats before they have tried the purity of the air in them by lowering a candle. If the candle is not extinguished, they know that they may de- fcend with fafety; for it is then certain that the fixed air has made its efcape. After the wine is calked, the fermentation dill goes on, though in a much flower degree, and a depofition of tartar takes place. The carbonic acid gas, that is now extricated, not being able to efcape, is abforbed by the liquor, and gives it its brilknefs, and that pleafant fharpnefs to the palate which it now has, inftead of the flat inftpid tafte which all wines have when firft made. The fame flow fermentation, accompanied with a depofition of tartar, and formation of carbonic acid gas, continues even after the wine is in bottles, and occafions the difference between old and new wine. In foine liquors the fermentation, and confe- quent formation of carbonic acid gas, is much more confiderable than in others, as in Champaign wine, in perry, or in cider; and hence their fparkling appearance and effervefcence, when uncorked. The quantity of gas formed in thefe cafes is fo great as only to be retained in combination with the liquor under great preffure ; and this preflure being removed by uncorking the bottle, part of the carbonic acid immediately affumes its gafeous form, aad flies cfff G 2 124f CARBON, OR CHARCOAL: As the brifknefs of all wines depends upon the prefence of carbonic acid, they will always prove flat and infipid, either when the fermentation is fo moderate, that fufricient carbonic acid is not formed, or when that, that is formed, is allowed to efcape. The former cafe never occurs when the faccharine matter fufficiently abounds, and atten- tion is paid to keep the liquor fufficiently warm. When, from want of this, it has happened, the fermentation mull be promoted by adding more fugar, and a fmall quantity of yeaft. Wines are more frequently flat in confequence of the gas being allowed to efcape when formed, and this both in the calked and bottled ftate. The fame may be faid of other liquors, as cider, perry, and more particularly beer. The calks ffiould al- ways be filled, or very nearly fo, and the tighter they are the better. The greater the refinance that is afforded to the new formed gas, the more will be ab for bed by the liquor, and the pleafanter it will be to the palate. In confequence of its being neceffary to make an opening to let in air when a barrel is tapped, the carbonic acid gas is allowed to efcape, and the beer or other liquor foon becomes flat, par- ticularly if the orifice is not clofed. Beer, that is thus rendered flat, may be made much more palatable again, by impregnating it with carbonic acid gas. An eafy mode of doing this in the barrel might, perhaps, be contrived ; but for 6 CARBONIC ACID GAS, ’OR FIXED AIR. 123 fmall quantities to be impregnated, as it is required for the table, nothing will anfwer better than au apparatus called Nooth’s apparatus, for making Seltzer water, which will prefently be noticed. In bottling every kind of wine, cider, beer, &c. 9 great care fhould be paid to the corking. The gas, as it is formed, exerts great force to efcape ; and if the cork does not fit very accurately will be fure to make its way out. The liquor will then never acquire the brifknefs, and lharp talle, that it ought to have. It is always better to lay bottled liquor on the fides than upright, for then the gas muff pafs through the liquor before it can efcape ; and bolides this, the cork is kept wet and fv/elled, and is much lefs liable to decay, which would thus communicate an unpleafant talle to the liquor. To make beer^ barley is foaked in water, and then laid in heaps fome inches deep, till the grain has germinated, and the germe, or new fhoot, is about two thirds of the length of the grain. It is then dried, to flop its growth, generally by artificial heat in kilns, when it is called kiln-dried; and fome- times in chambers, where the air is freely admitted, when it is called air-dried malt. The malt previously fkreened, that is feparated from the hulk, and germe, or new fhoot, which is called its culm, and then ground, is infufed in G 3 1 26 CARBON* OR CHARCOAL; boiling water in a mafh tub. The liquor* then drained off, is called fweet wort. It is next boiled with hops, to give it a pleafant flavour, and is cooled as fpeedily as poffible, to prevent its running into the acetous fermentation, and turning four. When cooled, it is put into large tubs or vats, and brought into the vinous fer* mentation, by the addition of yeaft. The fame circumftances take place as to the ex« trication of carbonic acid gas, when beer is in a ftate of fermentation, as when wine is made. In both it is the vinous fermentation, and in both the refult is a fpirituous liquor. The barley is firft made to vegetate, beeaufe it thereby acquires a greater quantity of faccharine matter; and this is a requifite ingredient in every cafe of vinous fermentation. As in every cafe of this fermentation, called the fpirituous or vinous, there is a fpirituous liquor formed, we may always procure the fpirit feparate, by diftilling fuch fermented liquor; and, accord- ing to the materials made use of, we obtain different kinds of fpirit , having different flavours, as well as different names. From wine lees is obtained the Rhenifh brandy. Trench brandy from the hufks and ftalks of grapes fermented. Rum from the fugar-cane. Gin, whifky, and other Britifli fpirits, from malt. Carrots, beet-root, potatoes, and feme other CARBONIC ACID GAS, OR FIXED AIR. 1£7 roots, by being fimilarly fermented, have been made to afford fpirits. And amongft the Tartars a fpiri- tuous liquor, called koumifs, is made by ferment- ing mare’s milk. Befides being extricated during fermentation, carbonic acid gas is formed in many inftances of combujtion . As mod inflammable bodies contain carbon, fo moil afford carbonic acid, when burnt, by the union of this carbon with the oxygen of the air. When charcoal is burnt, it is formed in fuch quantity, as to be made fenfible by its bane- ful effetts. We have before Hated, that it will not fupport life ; and many a p§rfon has been killed by not being aware of this circumftance, and that it is given out a wherever charcoal is burnt. It is very common to light a charcoal fire in cellars, and vaults, when wine is to be bottled off in cold weather ; and in fuch fituations there being no current of air to waft away the noxious gas, many have experienced its deleterious effeQs. In warm- ing and airing damp or cold rooms it is frequently burnt, and in many manufactories the workmen are a good deal expofed to the effluvia. In thefe, and in all other cafes, where burning charcoal is ufed, great caution {hould be taken, to remove the gas as effeftually as poflible, and for the workmen to be as little expofed to it. The firft effe&s that are experienced by a perfon G 4 1£8 CARBON, OR charcoal: expofed to this gas, are extreme latitude and drow- finefs. He foon becomes unable to fupport himfelf, and faints away. If he has not the power to remove from the effluvia, when he firft feels its influence, and is not fortunately removed fhortly after he faints, he remains fenfelefs, and is foon irrecover- ably loft. When a perfon is difcovered fuffering from this caufe, he fhould inftantly be removed to the open air, and the fame plan be adopted as in cafes of apparent death from drowning. If the perfon fhows any figns of life, as foon as brought into the air, the p refer ving a free circulation of air, and the dafhing of cold water on the furface of the body, to ex- til? a 61 ion of tl^e refniratory organs. \yill be fufficient. But, if he appears lifelefs, artificial refpiration with the double bellows, continued friftion, and the application of heat, muft be had recourfe to. If an eleftrical machine be at hand, a fhock fhould be paffed through the region of the heart. Bleeding, the ufe of emetics, and the admini- llration of tobacco glyfters, as recommended by fome phyficians, I look upon not only as unfer- viceable, but as likely to deiiroy what fmall fpark of life may yet remain. We have laid, that carbonic acid gas is given out by the refpiration of animals, as well as by com- buiiion. This is eaflly proved by breathing, through CARBONIC ACID GAS, OR FIXED AIR. 129 lime water ; for it immediately becomes turbid, which we have before Hated to be one of the pro- perties, and a diftinguifhing property, of carbonic acid gas. The caufe of it we fhall give prefently. This extrication of carbonic acid gas in breath- ing is another caufe, to be added to that of the absorption of oxygen, or the pure part of the air, why animals can live only a fhort time when confined in clofe veffels, and why we fo conftantly require the accefs of frefli air. From the greater fpecific gravity of carbonic acid gas, it is frequently found occupying pits, and* low fituations. It often occupies the bottom of wells, and therefore workmen ought always to be cautioned againft defeending into fuch places, with- out firft lowering a lighted candle. If the candle continues to burn, they may defeend with fafety ; but if not, it is fure to be dangerous. There are feveral caves and grottoes, in different countries, that are occupied, at leaf! near their bottoms, by this heavy gas. A man may often walk in them without any ill effefts ; whilft a dog, or other animal, breathing a ftratuin of air nearer to the ground, will foon experience unpleafant fymptoms. In mines this gas is called the cloak-damp, as in- flammable air is called the fire-damp. A lighted candle is a fufficient tell, to determine the prefence or abfence of the choak-damp ; but, for reafons G 5 ISO CARBON, OR CHARCOAL: before mentioned, it would be attended with great danger, where the fire-damp is prefent. In all cafes where the prefence of fixed air is likely to be attended with inconvenience, the fol- lowing rules fhould be obferved to obviate it. Where it can be done, it fhould be removed by ventilation. In rooms where charcoal is burnt, frefh air fhould be freely admitted. In mines, fires fhould be kept up near one entrance, fo as to caufe a conftant current of air through the mine; and, where it is prafticable, a ftream of water fhould be anade to flow through that part that is moft charged with the gas ; for water will abforb a confiderable quantity of it. The plan that is moft frequently applicable for removing this baneful gas, is to abforb it by means of lime. In apartments where it is prefent, tubs of water with a quantity of quick lime in it will be fufficient. In wells the fame mode will anfwer ; and, in mines, pits or pools of water may be im- pregnated with lime, and quick lime may be fprin- kled about the floors. Springs of water are fometimes met with, naturally impregnated with carbonic acid gas, as that of Seltzer, which is noted for its medical virtues. To imitate fuch natural waters, we have only to pour diluted fulphuric acid on powdered chalk, and fuffer the gas, that is extricated, to pafs repeatedly through water, till a fufficient quantity is abforbed, CARBONIC ACID GAS, OR FIXED AIR. 131 An apparatus, known by the name of Nooth’s apparatus, effe&s this purpofe with great eafe; and, when properly managed, without much danger of its breaking. When the mixture of the acid and chalk is carelefsly made, there is fo much gas fud- denly evolved, as frequently to burft the veffel, and inconvenience the operator. The way to prevent this accident, and the proper mode of managing the mixture is this. Firft put your acid in, and by in^ dining the apparatus, let it remain on one fide ; then drop in the powdered chalk, fo as to occupy the other fide of the veffel ; and always let it ftand a little inclined. Now, when you wifh more gas to be evolved, you have only to fhake it gently, fa as to wafh down a little of the chalk with the acid, and then return the veffel to its inclined pofition. By this means the evolution of gas will be gradual, and all danger of the apparatus burftingbe obviated. This Seltzer water, whether natural or artificial, is drunk with advantage in many cafes of indigef- tion, and in calculous or gravelly complaints. Water impregnated with carbonic acid gas is ena- bled to diffolve more lime than common water; and water thus charged depofits its redundant lime, when by expofure to the atmofphere it lofes its car- bonic acid gas. This is the caufe of all the calcare- ous incruftations, termed petrifa&ions, and all the ftala&ites formed in caverns. G 6 1 32 CARBON, OR CHARCOAL : The water in fuch fituations, being impregnated with fixed" air, diffolves more lime than it can after- wards hold in folution, when by expofure to the at- mofphere it lofes its air. As the water lofes its fixed air, therefore, it gradually depofits its lime ; and if there happens to be mofs or any other fub- ftance in the ftream, it becomes incrufted with the lime, whilft it retains its natural form. Carbonic acid, like other acids, enters into com- bination with the earths , and alkalies , forming neu- tral falts. When united to lime, it forms chalk, or lime-ftone, or marble ; and thefe fubftances, when again deprived of the carbonic acid, are reduced to lime. For the purpofes of making mortar, lime- ftone is deprived of its carbonic acid by heat ; the ftone and fome kind of fuel being burnt together in a kiln. The carbonic acid gas being thus driven off by heat, leaves the ftone in the ftate called quick lime, which is a cauftic corroding fubftance. When expofed to the air, it gradually attra&s the carbonic acid gas, which is always prefent in a fmall proportion, and is thus reconverted into chalk or lime-ftone. It is now mild, and inert, inftead of being cauftic, and is no longer fit for making mortar. The extrication of carbonic acid gas, when lime is burnt, makes it a very unhealthy employment to be engaged conftantly in lime-kilns ; and many ac* CARBONIC ACID GAS, OR FIXED AIR. 133 cidents have happened, from perfons deeping too near the burning lime. It is the great difpofition that lime has to unite with this gas, that caufes the turbid appearance in lime-water, when expofed to the gas. Lime by it- felt is foluble in water, but chalk is not; when therefore the lime in the lime-water has attra&ed the carbonic acid gas, and thus become chalk, it is depofited, and caufes the turbid appearance. As the lime will gradually attract the gas from the air, lime-water fhould always be kept in bottles well corked, otherwife the lime is feparated, as ap- pears by the pellicle on its furface, and the lime- water becomes only common water. We have now finithed the confideration of car- bonic acid gas, and {hall in the next effay treat of other combinations of carbon. 134 ESSAY XIII. CARBON, OR CHARCOAL ; COALS, OILS. The compounds remaining to be noticed, which have carbon for their principal ingredient, are coals of different kinds, and oils. The bitumen of coals, as well as oils, is a compound of carbon and hydro- gen, with a fmall proportion of oxygen, and fome- times of azote. The foot, which they afford, is chiefly carbon; and the more {lowly or incom- pletely they are burnt, the more foot they afford. That from oils forms lamp-black. Whatever be the origin of coal, whether vege- table, animal, or mineral, and how numerous fo- ever its varieties, it has certain uniform characters, and differs but little in its chymical qualities. Coal is a compound of oily or bituminous matter and fulphur with an earthy bafe, generally alumi- nous, argillaceous, or clayey, which are fynoni- mous terms. It is a kind of fchiftus impregnated with bitumen and fulphur. And this fchiftus is found thus impregnated in various degrees. It is only when it contains fo much bitumen, as to make it burn with facility, that we denominate it coal ; but in the fame mountains, that we find CARBON, OR CHARCOAL: COALS, OILS. 1S5 coal in, are other ftrata of the fchiftus lefs impreg- nated with bitumen, and thefe are known under other names. Coals are commonly found in hilly fituations, and always under ftrata of grit, which is a mixture of fand and clay ; or under fchiftus, which is clay hardened, and fplitting into layers, forming either Hates, or a fubftance called Olivers, according to its fra&ure. • The coal is found in thefe mountains in ftrata, from a few inches to fome feet in thicknefs, and al- ternating with ftrata of grit or fchiftus. The beds of coal run in various directions, generally with a dip or inclination from the horizontal pofition. They are frequently intercepted by columns of other matter ; and the continuation of the bed may be either higher, or lower, than the part from which it has been, or feems to have been, feparated. The continuation too fometimes takes the fame, fometimes a very different degree of inclination, or dip. It generally happens that the firft ftratum of coals, that we come to, is not worth working, either from the inferior quality of the coal, it containing too little bitumen, or from the ftratum being of too little depth. From the degree and dire&ion of the dip, and the level of the country, much information is to be ob- tained, concerning the proper place for opening the 1 36 CARBON, OR CHARCOAL! COALS. pit. A variety of circumftances require to be taken into confideration, to work a coal mine to the great- eft advantage ; or to determine, whether a mine ought to be worked at all. Even in countries, or in thofe parts of the country, where none has been found, very probable conjeftures may be formed concerning its prefence, by attending to the foil, to the general appearance of the country, and to the kind of clay, fand, or other earth, that is found, when the foil is removed. There are certain ap- pearances that indicate its prefence, its value, its extent ; and others, that point out the proper mode of working the mines, when difeovered. Thefe indications are fubjeft to variations ; and thefe va- riations are often appreciable by certain other rules. The buftnefs of mining is therefore an intricate art ; and none ought to enter upon it, without a practi- cal knowledge of it, or the aftiftance of pra&ical miners. When a ftratum of coals is come to, that is con- fidered worth the working, it is dug out from the fuperior and inferior ftrata, which are generally grit, or fchiftus, and which are then termed the roof, and floor. In doing this, care is always taken to leave columns of the coal Handing here and there, fufficient to fupport the roof. When the roof is fhivery, it is frequently neceffary to fupport it with a ropf of timber. Thefe mean’s being taken' to fup- port the fuperior ftratum, the miners proceed to CARBON, OR CHARCOAL: COALS. 137 very confiderablc diftances from the original pits ; and occafionally new fhafts or pits are funk, to fa- cilitate the removal of the coals, and to afford a proper ventilation in the mines. The varieties of coal have been very differently arranged by different authors ; fome dividing them according to their external appearances ; fome as to the fituations in which they are found ; others ac- cording to the manner of their burning ; and ftill others as to the peculiarity of their fraflure. The faft is, that almoll every mine affords a coal, differing in fome refpefts from that of others ; and, although the inland coal is generally very different from the Newcaftle, which we call fea-coal, yet both vary fo much, as procured from different mines, or even different parts of the fame mine, that one parcel of inland or of fea-coal fliall differ very coniiderably from another, both in its burning, and its general appearances. The different manner in which coals burn de- fer ves notice ; and, if any arrangement of the vari- eties of coal is to be made, this affords the beft grounds for it. The difference does not depend wholly upon the proportion of bitumen, but partly upon the kind, whether it is more or lefs volatile, and whether it is more or le^s eafily feparated from the earthy hafe. As the coal varies in rhefe rcfpecis, it comes under, 15$ CARBON, OR CHARCOAL : COALS. or approaches to, more or lefs, one ©f the follow- ing divifions. The firft includes fuch coal as affords a very con- fiderable flame, and burns with fo much rapidity,, as only to require being lighted, like a candle, to continue its combuftion. This contains moll bitu- men. The candle or cannel-coal is of this kind. The fecond, which includes mofl of the inland coals, called by fome fplit coal, contains fuch as' burn with more or lefs flame, but require to be kept in a flate of ignition by furrounding fuel, and leave a larger quantity of afhes, having more of the fehiftus in their compofitionr The third divifion includes thofe coals that unite or cake together when heated, in confequence of the extrication of their bitumen. Of this kind are the fea or Newcaftle-coals. This property of cak- ing does not feem to depend upon the proportion of the bitumen, but upon its being extricated by a: lefs degree of heat, than is fufficient to inflame it ; for coals of this kind often afford as much afhes as the inland coals. The laft divifion contains what is called blind coal, which affords neither flame nor fmoke, but when kindled makes a brifk and clear fire like coke* The Kilkenny coal is of this fort. In its external appearance it fometimes refembles the cannel-coal, and fometimes the fplit or inland coal. The pecu- liarity of this kind feems to depend upon its pof- CARBON, OR CHARCOAL! COALS. 139 -fe fling a lefs inflammable bitumen, or to fpeak more corre&ly, a lefs volatile bitumen ; for, as flame is nothing but the inflammable body ignited in a ftate of vapour, the quantity of flame muft depend chiefly on the volatility of the fubftance. When coal is piled up, ignited, and the fire then fmothered, as in making charcoal, the refult is a light porous fubftance, called COKE, which burns much like charcoal without flame or fmoke. It is ufed in drying malt, and other operations, where the flame and fmoke would be injurious. In fome places furnaces or ovens are built for making coke, and the fires are put out by dampers, when it is fuf- ficiemly burnt* In this operation the more vola- tile, oily, or bituminous matter is exhaled, and, if collefted, as in fome manufa&ories is the cafe, it forms a very excellent tar. It is the caking coal that makes the beft coke, for it is neceflary that the pieces fhould be at firft fmall, that the heat may ex- tricate the bitumen without confuming it ; and that it fhould afterwards run to ether into larger maffes, that ic may be leh porous and fpongy. At Newcaftle, the coal drift, that is too fmall for common ufe, is burnt into coke, and forms excel- lent fuel. Might not the coal dull in inland mines, which will not anfwer for making coke, be worked up into combuftibie bricks with a fmall proportion of clay, and, if requifite, a fmall quantity of fome inflammable fubftance, as the coal-tar, fo as t® UO CARBON, OR CHARCOAL; COALS. make a neat and perhaps economical fuelJFor our open fire-places? With refpeft to the origin of coals , the moft probable fuppofition is this. That the trees and other vegetables, that are carried down the ftreams into the ocean, are colle&ed in ftrata at the bottom, together with the immenfe quantity of fea weeds, that grow there, and perhaps the fea animals too. That they are afterwards covered with clay or land ; and, undergoing a gradual decompofition, form fo many ftrata of coal, placed alternately with ftrata of clay or fand. That the coal itfelf is of vegetable origin, is fairly inferred from a variety of vegetable remains and im- preffions, that are found both in the ftrata of coal, and in the earthy ftrata above and below them. That it is of fubmarine origin, alfo appears from the pre- fence of (hells, and other productions of the ocean. The popular opinion, that coals grow like vege- tables, fo that the mines, that are worked out, may be opened, and worked again after a feries of years, is too erroneous to need any formal refutation. We need not, however, be alarmed for the wants of future generations, as to this ufeful article. The immenfe beds of coal yet untouched, will fupply marly thoufands of generations to come ; and there is no doubt but the fame procefs, that produced what we at prefent ufe, is ftill continued, and that fome future convulnons will bring to light new coal CARBON, OR CHARCOAL; OILS. 141 mountains, perhaps from the bottom of the fea; for that, it is mod probable, is the place where nature has fixed her laboratory for preparing this fuel for far diftant ages. Oils are a well known vegetable production. They are either fixed, or volatile; the former con- taining mucilage, and the latter an aroma, which is different in every different oil. They are obtained either by expreffion, as the olive oil, and linfeed oil, among the fixed; and the oil of lemons among the volatile kind ; or they are obtained by diftil- lation, as the oil of peppermint, of thyme, and indeed m@fl of the volatile oils. When the fixed oils are expofed to the air, they abforb oxygen, and become rancid. The oxygen in this cafe unites with the mucilage of the oil; and therefore fuch as are deprived of their mucilage are not liable to become rancid. The feed of the flax, from which linfeed oil is obtained, contains fo much mucilage, that it is neceffary to torrefy or roafl it, previoufly to ex- preffmg the oil. This deftroys the mucilage, and hence linfeed oil hardly ever turns rancid. If oil of almonds is well agitated with water, its mucilage is partly feparated, and the oil is lefs fub- ject to become rancid. Although oils, that are deprived of their mu- cilage, do not attraft oxygen from the air, and con- fequently. do not turn rancid, yet they may be made 142 CARBON, OR CHARCOAL; OILS. to unite with it in other ways, and then they be- come drying oils . Drying oil is generally made by the painters, by boiling a calx of lead, as the litharge, in linfeed oil. The oil attrafts the oxygen from the metal, and thus becomes a drying oil. If an oil is ufed that con- tains mucilage, the latter is feparated in boiling, and fwims at the top; but, fuch as contains no mucilage, makes the beft drying oil. When the volatile oils are expofed to the air, inftead of becoming rancid, they become thick, and refmous, and lofe their aroma. This alfo arifes from the abforption of oxygen ; and the fame effeft is produced by forming the combination in other ways, as by adding an acid to the oik The ufes of all the oils arc too well known to require enumeration. Tallow and fat, which are animal oils, differ from the vegetable oils principally in containing a peculiar acid, called the febacic acid. 143 ESSAY XIV. PHOSPHORUS. Phosphorus is one of the chymical elements* It is a folid fubftance, but fo foft as to be eafily fcraped or cut with a knife. It is generally of a flefh colour; and when pure it is tranfparent. In the air it emits a white fmoke, a peculiar fmell, and a beautiful though faint light, which becomes vifible in the dark. It inflames by the application of a gentle heat, and then burns with a very brilliant flame. This curious fubftance is of animal origin. It exifts in a compound ftate in all kinds of bones, and likewife in confiderable t quantity in urine. The means of obtaining it from either are not very Ample, and the procefs cannot be well under- flood until we have treated more at length of its properties. If any device is traced with a flick of phofphorus on paper, as with a crayon, every line becomes beautifully luminous in the dark, and continues fo for fome minutes. If held before the fire for a moment the brilliancy is increafed; but this mull he done with caution, as very little heat is required 144 PHOSPHORUS. to inflame the phofphorus, and then the paper will take fire. By handling the phofphorus, part of it adheres to the fingers, and covers them with the fame light. This is not at all dangerous, as no fenfible heat is emitted; but if you rub your hand much, with a view of getting rid of it, the heat excited by the frifiion will inflame the phofphorus; and if there is much of it, it will then burn the hand. 1 have obferved great inconvenience from perfons getting fmall pieces of the phofphorus under their nails, by handling it injudicioufly ; for, when they have approached the fire to warm their hands, fuch pieces have inflamed and given great pain. To prove how eafily phofphorus is made to burn, rub it on a piece of tow, wrap this tow round a Florence-flafk, or other glafs veffel, and pour hot vrater into it. The heat of the water will inftantly inflame the phofphorus and the tow on the outfide. Phofphorus is foluble in oils, particularly the volatile oils, which it renders luminous like itfelf. This folution may, without danger, be rubbed about the face and hands, fo as to render them luminous. The folution of phofphorus in ether when thrown upon boiling water, exhibits a pleafing appearance; the heat inflaming the phofphorus, and rendering it beautifully bright. This folution is alfo luminous of itfelf. PHOSPHORUS. 145 Phofphorus is likewife foluble in hydrogenous gas, or inflammable air, which it renders luminous. This very amufing compound may be obtained by boiling a little phofphorus in a folution of pure potafh. The water is decompofed in this experi- ment, and affords the inflammable air. The retort fliould be very nearly filled with the folution, other- wife the gas will inflame, and diminifhing the volume of air in the retort* occafion the water to rufh in from the trough. When this phofphorated hydrogenous gas is in contaft with common air it emits light, and, like phofphorus itfelf, undergoes a flow combuftion; but when it is mixed with pure air, (oxygenous gas) it immediately detonates. To make the phosphoric match bottles, nothing more is neceffary than to drop fmall pieces of dry phofphorus into a common phial, gently to heat it till it melts, and then turn the bottle round that it may adhere to the fides. The phial fliould be clofely corked, and when ufed, the match (a common brimflone match) is to be introduced, and rubbed againft the fides of the phial. It thus ac- quires a portion of phofphorus, which inflames on being brought into the air. When phofphorus is confumed either by the flow combuftion, that fpontaneoufly takes place when it is expofed to the air, or by the more rapid one produced by inflaming it, the pure part of the H 146 PHOSPHORUS. air (oxygen) combines with the phofphorus, and forms phofphoric acid. This acid, like others, unites with the fimple earths and alkalies, forming neutral fairs. It is the compound refuiting from its union with lime that forms the hard offeous matter, that is the bafis of all bones. The urine contains this acid, united both to lime and to the alkalies. After being made acquainted with thefe fafts, we fhall more eafily comprehend the nature of th£ procelfes, by which phofphorus is obtained. To obtain it from bones, feleft the hardeft; burn and then pulverife them. To this powder add half its weight of vitriolic acid, ftir it well, and then leave it for two or three days; after- wards add water gradually, and ftir the mixture; when the powder has fubfided, decant the fuper- natant liquor, and evaporate it to drynefs. Upon this dry extraft pour boiling water as long as it continues to tinge the water, and then evaporate this folution to the confidence of a thick firup. To this extraft add juft fufficienfe water to diffolve the phofphoric acid, and filter through linen. Laftly, mix this extraft with powdered charcoal, and diftil from an earthen retort, the neck of which is immerfed in water. The phofphorus will drop into the water, and may be worked into form with the fingers. Some prefer converting the phof- phoric acid into a glafs, which is done by expofing PHOSPHORUS. 14*7 the ext raft in a crucible to a ftrong heat. To ob- tain phofphorus from this glafs, nothing more is neceffary than to powder it ; mix it with an equal quantity of powdered charcoal, and diftil. The fulphuric acid in this procefs combines with the lime, and detaches the phofphoric acid, which, when mixed with the charcoal, is likewife decom- pofed ; its oxygen uniting with the carbon, forms carbonic acid gas, or fixed air, whilft the phofpho- rus comes over in its pure ftate. To obtain phofphorus from urine, it is generally recommended to evaporate the urine, and then diftil with charcoal ; but a lefs troublefome, and lefs difagreeable way is, to add a folution of lead in muriatic acid to frefh urine, until it caufes no more fediment to fall ; then filter the whole through two or three folds of linen, and mix up the fedi- ment, that is left on the filter, with powdered charcoal into a pafte. This pafte diftil led in an earthen retort, with a pretty ftrong heat, affords the phofphorus. The muriatic acid here difengages the phofphoric from both the lime and the foda, with which it was combined, and the fediment is a phofphat of lead which is afterwards decompofed by the charcoaL It is here that I fliall notice what may be termed NATURAL phosphori; by which' I mean fuch bodies as naturally emit light, fimilar to that, and regulated nearly by the fame laws as that of phof« H 2 14 : 3 PHOSPHORUS. phorus.. They will include living animals, that poffefs this property, dead animal matter, and de- cayed vegetables. Of living animals, that appear luminous in the dark, there are in this country two land infefts ; and, on our coaft feveral marine infefts and fifhes. The two land infefts are both vulgarly called glow-worms, but are very different both in theil* manners and appearance. The one is a fcolopen- dra ( fcolopendra eleffrica), fomething like the cen- tipes, being a thin and flattifh worm with a great number of feet. It is often found in houfes about old furniture. •» The other is a foft, broad, and flat infeft, fome- thing like the millepes (the woodloufe or old-fow), extended and flattened. It is apterous, or without wings, but is the female of a winged infeft of the beetle tribe {lampyris nottiluca)* The infe£l is very common on the heaths in Norfolk, and in fimilar fituations elfewhere. The light emitted by this infeft proceeds from the three laft rings of the abdomen, is of a beautiful fulphur colour, and appears, when accurately examined, to proceed from diftinft but numerous fmall globules within the abdomen, which are probably the ova or eggs. It is a fubjeft worthy of further attention from the naturaliff. The marine infefls will be noticed in treating of the luminous appearances of the fea, which will ' fall prefently to be confidered. PHOSPHORUS* 149 In other countries, particularly in warm climates, there are feveral luminous infe&s, and much larger ones than we have here. Such are the lantern-fly of China, and the candle-fly or fire-fly of the Weft Indies, which emit a very ftrong light from the probofcis €r fnout. Of dead animal matter almoft every kind has at times been obferved to be luminous, as whole joints of mutton, and venifon, pieces of veal-bones, lob- Hers claws, &c. ; but what peculiar circumftances determine thefe fubftances to emit light at one time, and not at another, have hitherto eluded our inqui- ries ; for, although they never fhine, but when in a ftate of putrefaftion, they more frequently pafs through the whole putrefattive procefs without af- fuming this appearance. There are other fubftances that conftantly fhine, when in a certain ftage of putrefa&ion. Thefe are various kinds of fifh, as mackerel, herrings, whitings, and fome others, which will he noticed in confider- ing the caufe of the brightnefs of the fea. In the vegetable world, rotten wood, when in that light fpongy ftate called touchwood, is the moft remarkable. This requires moifture to emit its phofphonc light. It is yet uncertain, whether the accels of air is, neceffary to fupport the light. Boyle fays, that it ceafed to fhine in an exhaufted receiver; but Achard, a French chymift, afferts that it continued to. emit light in that fituation. When H 3 PHOSPHORUS. uo it becomes quite dry, its light is extinguished, but reappears, when the wood is moiftened. The colour of the light in all thefe inftances is pale blue, exaftly refembling that of phofphorus. It is in all cafes, except that of the rotten wood, increafed and rendered more intenfe b)A immerfing the luminous body in oxygen gas, and is extin- guished by immerfion in azotic, or in nitrous gas. It is in all cafes too, except that of the wood, at- tended with the extrication of an oily matter, which adheres to the fingers, and makes them appear lu- minous. Which circumftances tend ftrongly to fupport the opinion, that the light is emitted in confequence of the formation of a phofphorated oil, or folution of phofphorus in animal oil. The opinion of fome modern chymifts is, that the light is a conftituent part of the fifh, but the necefiity of the prefence of oxygen gas makes it much more probable that the fixation of oxygen, with the confequerit reparation of its light and heat, is the true caufe of its appearance. W e acknowledge this to be the fource ot light in common combuf- tion, and in the flow cornbuflion of phofphorus ; why then look for any oilier in the infiance before us, where the prefence of oxygen gas is equally necefiary ? Some have doubted, whether oxygen gas is necefiary to the emiflion of light from phof- phorus ; but this I fatisfaftorily proved to be the cafe by the following experiment* A piece' of PHOSPHORUS. 151 phofphorus being inflamed in a jar of common air, inverted over water, burnt readily, till nearly all the oxygen gas was confumed. The fame piece, being again inflamed in the fame fituation, burnt for a few moments longer, and fo a third time. Even after this the phofphorus fhone for a few hours, but at length its light was wholly extin- guifhed. After fome hours, the phofphorus Hill remaining dark, frefh air was admitted into the jar, and the light immediately reappeared. In rotten wood, that is luminous, as moiflure feems neceffary, and oxygen gas not fo, a different procefs, not yet afcertained, is probably the caufe of the phenomenon. A.s the luminous appearance of the fea has fre- quently attrafted the notice of navigators ; and as, in eohfequence of its affuming a variety of appear- ances, it has been very differently explained; I fhall enter more into detail upon this point, and beg leave to do it in the words of a differtation which % l wrote feveral years ago. Dissertation on the luminous appear- ance the sea, read before the Natural Hijlory Society of Edinburgh , in December , 1796, The luminous appearance of jhe fea is fo com- mon, as well as curious a phenomenon, Ahat alrnoli H 4 1 52 PHOSPHOR U S. every one, who has been on the fea in a fummer’s evening, particularly in warm climates, mull have obferved it. Its variety of appearances has however given rife to fuch different deferiptions, and contrariety of opinions refpe&ing' its caufe, that on a flight view it appears almolt impoffible to reconcile thefe various accounts, and afeertain its real nature. To attempt this, however, is the object of the prefent paper. That celebrated philofopher Boyle did not let this curious phenomenon efcape his extenfive re- fearches into the operations of nature. But, learn- ing from fome, that the fea was only luminous when diflurbed and agitated ; from others, that they had feen the whole furface of the fea covered with a bright light, like burning fulphur, as far as their view extended ; whillt others again deferi bed the light, as being confined to certain parts of the furface, other parts, not tar diflant, being not at all luminous; he was fo confounded wfith thefe 4 various accounts, that he concludes by referring the phenomenon to fome cofmical law, or cuitom of the terreftrial globe. Father Bourzes in His voyage to the Indies, in 1704^, fays,, that he could fometimes (hftinguifii in the wake of the (hip the particles, that were lumi- nous, from thofe, that were not fo. Some, he fays, were like points of light, others like liars; PHOSPHORUS. 1 55 fome like globes of a line or two in diameter, and others as large as a man’s hand. Sometimes all thefe different figures were vifible together ; and at other times there were what he calls vortices of light, appearing and then difap- pearing, like flafhes of lightning. Not only the wake of the ihip produced this light, but fifties alfo m fwimming left a luminous track behind them, lo that their fize and fhape might eafily be diffinguifh- ed. He remarks too, that this appearance is greateft when the w T ater is fait eft and fulleji of foam . In thefe observations are I think aefcribed all the appearances that have been obferved, and no- ticed by others. And, I think, that they may be reduced to two kinds, which differ effentially not only in the appearance of the light, but alfo, as I fhall afterwards endeavour to £how,.in their caufes. The firfl; kind includes thofe cafes, where the furface of the water appears- luminous without agitation ; and where, when agitation is neceffary, to produce a luminous appearance in the body of the water, the part illuminated affumes no deter- minate figure, but gives out its phofphorefcency wherever the agitating caule prefides. Of thrs kind are the expanded lights mentioned by Boyle, and the luminous track left by the fifh in fwimming, as defcribed by father Bourzes. 1 he feconcl divifion includes all cafes, where the light is of a determinate figure, and where it ap- H 5 154 PHOSPHORUS. pears and difappears repeatedly without any apparent caufe. In mod of thefe cafes agitation will produce the light, though it is not always necelfary. Of this kind are the beautiful fcintillations ob- ferved by every mariner, and met with more fre- quently than any other fpecies, in our own latitude in the fummer feafon ; and likewife the fiars and globes of light mentioned in the narration of mo- dern navigators. Let us now proceed to invefligate the caufe of this phaenomenon. The Abbe Nollet and feveral others, having examined the fea water near Venice, which in the dark was feen to contain luminous fpots when agitated, thought they found fmall in- fects, to which they attributed the light. M. le Roi, examining foine water which poffeffed the fame property, was perfuaded that it was not entirely owing to infe&s ; for the luminous fpots, which he took up, were round fub fiances of the fize of pins’ heads, which had no appearance of being animals. M. Dagelet too obferved fimilar bright bodies, which he fufpefled to be the fpawn of fome kind of fifh. M. Canton, from fome experiments which he performed, and which we fhall have occafion to mention presently, attributes the light of the fea to putrid fifh. Count Gregorius Razamoufky afcribes the light, PHOSPHORUS. 155 which is obferved in the fhip’s wake, to phofpho- rical gas, difengaged by the friStion of the waves againft the fides of the vefTel. Mr. White fuppofes that it is fometimes owing to large fifh having the property of filming whilft alive ; but, as this property is generally confined to the fmaller animals, it was probably owing in the inftances, to which he alludes, to the fmall pa- rafitical infefts, that burrow under the fcales of fifh, and which poffefs this phofphorefcent quality. I have often feen thefe little animals burro win o’ o under the laminae of oyfler fhells. From the above obfervations, it appears that the light in the fea is fometimes derived from living, and fometimes from dead and putrid animals. For reafons, which- 1 {hall give prefently, I . fufpefl that our fir ft kind of luminous appearances is always owing to putrid fifh, and the fecond to living ani- mals, under which I include the {pawn of fifh. Let us now confider thefe caufes separately. That putrid fifh will not only fhine itfelf, but communicate this property to fea water, or a io- lutibnof common fak in water, was, I believe, fi rft obferved by Dr. Beal, in 1665 ; but Canton firft made experiments with a view of afeertaining its caufe. 1 he appearances in thefe experiments are fo firm- lar to thoie obferved in tlie fea, which we have H 6 156 PHOSPHORUS# included in our firfl divifion, that I am induced to attribute them to the fame caufe. M. Canton immerfed a herring, which appeared very bright in a darkened chamber, into fait water, and the furface of the water became inflantly lumi- nous ; the light too was increafed by agitation. When he repeated the experiments with whitings, inftead of herrings, he remarks, that the water did not appear luminous, unlefs when agitated, but that when a flick was drawn through the water, it left a luminous track behind it. I have obferved the fame when mackerel are ufed. This difference between the herring and the whiting is a curious faft, but what I cannot fatisfacdorily explain That the light given out by dead fifh is owing to the changes it undergoes during putrefaftion, may, J think, be fairly deduced from the following ex- periments. Mr. Canton immerfed a whiting (frefli caught) in fea water, and it gave no light, till the next day. I have obferved that herrings emit very little, if any, light, till about twenty-four hours after death t : and a mackerel, which I did not procure till a day after it was caught, fhone very little ; * May it not depend upon the oily matter of the herring being fpe- cifically lighter than the water, and therefore fwimming on the Mil ace, whilft that of the whiting, being nearly the fame with it, is lufpended in the body of the water ? t Herrings, and, I believe, mackerel, fhine conliderably when fwhnming in the water, but ceafe to do fo when firft killed. PHOSPHORUS. 167 but the light of this, as well as of the- herrings* continued to increafe till fixty or feventy hours after death. The tail, fins, and head always fbine firft, and have generally ceafed to fhine,. before the more flefhy parts attain their greateft luftre. Gene- rally, by the end of the fourth day, the whole has ceafed to emit light. Mr. Canton kept a whiting in a ftrong brine for three days, and it did not fhine ; when he took it out it was quite frefn. I immerfed a piece of mackerel, that fhone at the time very bright, in nitrous gas, and in about five minutes it had loft its brightnefs, which it regained in about five minutes alter it was taken out. In the next experiment, being allowed to remain for five minutes in the gas, after its- light had dis- appeared, it did not regain its brightnefs in a quarter of an hour, at which time I left the laboratory ; but, on my return fome hours after,, it was fhining nearly as bright as at firft. * This effeft of nitrous gas I attribute to its welf- known antifeptic quality ; and this, with the pre- ceding experiments, fufficiently proves, that the fifh emits this light during a certain ftage of its putrefaction only.. On what the extrication of light immediately depends, it is more difficult to afcertain. From the fimilarity in its appearance, I’ think it probable, that the formation of fome combination of phofphorus is the immediate caufe ; and from the fait water, ren- 15 $ PHOSPHORUS. dered luminous by fiih having its fur face covered with oil, and from a greafy fubftance adhering to the fingers, which continues to emit light after touching luminous fifh, or water rendered luminous by them, I rather fufpefl: it to be a phofphorated oil, than a gas. We (hall now proceed to confider the caufe of our fecond divifion of luminous appearances, which I have before ftated to arife from living bodies. From the obfervations of M. le Roi and M. Dagelet, it feems to proceed in forae infiances from the fpawn of fifh : but the bright fparkling, fo often obferved on agitation, is more commonly owing to fmall infefts, frequently to a fpecies of mono cuius, as that deferibed by the Abbe Nollet, found in the water near Venice, and that by M. le Riville in the water near the Maldivia iilands, in the Eafi Indies. The fame, or a very fimilar infeft, has been lately found by a friend '* of mine in the fait water of a river in Cambridgefhire, about ten or twelve miles from the fea. Tnis gentleman procuring fame of the water, which contained thefe luminous fpots when agitated, took it into a darkened room, and dipping his hand into the water, feveral of the bright fpecks adhered to it. Thefe he carefully took off with the point of a knife, and dropped into a giais of clear frefh water, where they continued to (bine * Mr. William Skrimlhire, a very accurate and attentive oMervev of nature.. PHOSPHORUS. 159 for a moment. This water, when viewed in the light, was feen to contain fmall fpherical tranfparent bags, which, when examined through a microfcope, were found to be in lefts, very like the common monoculus. M. le Riville fays, that the parts of the infeft, that give the light, are bunches of fmall bodies in its pofterior part, which he fuppofes to be the eggs. Thefe little animals never admit light but when the water is agitated, as by the motion of a veflel, or the oars of a boat, which come out of the water every time beautifully befpangled with brilliant fpots ; or by throwing a Hone or other body into the water, in which cafe many of the infefts become vifible. This circumflance has induced Dr. Darwin to believe, that this kind of light is not produced by infefts ; but it appears to me a very inconciufive argument ; for it is poflihle that the infefts may only appear luminous when hurt or a floated by fear, which will account for their {Lining only when the water is difturbed ; or, what is Hill more probable, the agitation may produce the light, by expofmg the infefts to the contaft of the air, which may be neceffary to their {Lining, as it is to the light oi phofphorus and other phofphorefcent fubfiances. There are feveral other marine animals poITeffing this power, which may therefore occafionajly prove the caufe of this phenomenon, viz. the Aiedufq 160 PHOSPHORUS. fimplex , the phofphorical property of which was even known to Piiny; the Dagyfa , firft difcovered by Sir J. Banks and Dr. Solander, off the coaff ot Galicia, which, apparently, from the account given in Hawkesworth’s Voyages, emits its light without the intervention of agitation ; Garcinium Opalinum , difcovered by the fame gentlemen ; the Nereis Nocticula; the Pholas , well known by the experi- ments made with them by the Bolognian academi- cians ; the Pennatula Phojphorea ; the Cancer Fulgens'; and, I believe, fome other fpecies of Medufa . For what purpofe thefe marine animals are en- dowed with this property, has not been afcertained. The female Lampyris Noctiluca (common glow- worm) poffeffes its fhining property for the fake of attradling the male, which being a winged in left has very different habits from the female, and would otherwife have difficulty in difcovering her haunts. Another natural phaenomenon which the proper- ties of phofphorus enable us to explain is, the will-o’the-wifp, or ignis fatuus. This luminous appearance is a -blue light, often of a columnar, often of other fhapes, very mova- ble, generally having a tremulous motion, dif- appearing and reappearing fuddenly ; and it is moftly reprefented as changing its fituation inftan- taneoufly, and appearing in different and diftant fpots. It is ufually met with in heathy or boggy PHOSPHORUS. 161 lituations ; and there is a prevailing opinion amongfl the vulgar, that it has the power of attracting and milleading travellers into bogs and miry places. The faft is, that many perfons mi flaking fuch an appearance for a light in fome houfe, have made their way towards it, and not difcovered their miftake till they were finking in a fwarnp. To a more attentive obferver, thefe ignes fatui bear all the appearance of ignited vapour ; and it is now very well known to be phofphorated hydroge- nous gas, or phofphorus diffolved in inflammable air, which I have before mentioned as poffefling the property of being luminous in the dark. This gas is extricated from a mixture of animal and vegetable matter, in a Hate of putrefaction, a circumftance that rauft frequently occur in marfhy places. A fimilar light has been frequently obferved in church-yards, and been fuppofed by the ignorant to be Something fupernatural. From inch a circum- fiance, which fcience teaches us to account for by natural laws, many a perfon has been fully perfua** ded that he has feen fomething fupernatural ; and fuch has often been the origin of the moll wonderful ghofl and apparition ftories. The human mind feems prone to attribute to. Supernatural agents whatever is not within its reach to comprehend. It is therefore amongft men of 1 62 PHOSPHORUS. weak and unenlightened minds, that we find molt inftances of a belief in the appearance of apparitions. But ought we not to be more humble, and ac- knowledge our ignorance ? When we meet with a vifible appearance that we cannot explain, or hear a noife that we cannot account lor, would it not be more becoming in us to, attribute it to fome natural eaufe, that from our confined knowledge we are unacquainted with, than to conclude that it is inex- plicable by natural laws, and muft be fomething fupernatural, becaufe we are ignorant of its eaufe? How many people are ignorant that there is a peculiar gas, often extricated from putrid matter, which burns of itfelf, and appears luminous in the dark ! and to us, who know the faft, how abfurd, how prepofterous it appears, that fuch people fhould therefore attribute fuch an appearance to the agency of fupernatural powers ! It is prepoflerous, but furely not more fo, than for us to attribute to the fame powers other occurrences which we cannot explain ; and yet many, whofe minds are well in- formed, are too apt to make fuch an inference. I cannot avoid bringing forward another argu- ment againft the probability of every tale or ftory that tends to inculcate a belief in the agency of fuper- natural powers in thefe, and fnnilar occurrences. It is an argument that I have obferved more fre- quently than any other to difeourage fuch belief, and this induces me to notice it. PHOSPHORUS. 163 Is it at all probable, that the eftablifhed laws of nature, laws which the Creator himfelf has eflablifh- ed and ordained, fhould in any inflance be fufpend- ed, or others appointed, unlefs for the effefting of fome grand, fome important objeft ? Is it likely, I afk the fuperflitious narrator of the {lory, that fuch means fhould be had recourfe to, for the purpofe of frightening and terrifying any one ? And yet fuch in general, if the tales were true, would feem to be the only efiFe6l, and the only objeci of this deviation from fixed and eftablifhed laws. Or is it probable, that fuch extraordinary means fhould be adopted, even to alarm the conference, and to punifh or reclaim an individual finner ? No, be affured the confcience of the wicked man needs no fuch fpur to increafe its poignancy. It is ever on the alert, and its fling will, without fuch inter- vention, at times be felt by the moll hardened and abandoned profligate. And as to punifhment, it is not in this, but in the world to come, that the deeds of the wicked will be judged, and their punifhments awarded. 164 ESSAY XV. SULPHUR, OR BRIMSTONE. Sulphur, or brimftone, is an inflammable fub- flance, found alone or combined with other bodies, in a variety of fituations* In volcanic countries it is found almoft pure, having been volatilized and thrown out by the volcanoes. In fuch fituations the earth and Hones, in which it abounds, are diftilled, and the refult oi this diftillation is brought to market as crude fulphur. By fufion and calling in moulds, it forms roll brimftone ; and by fublirning or volatilizing it with a gentle heat in clofe chambers, we obtain the flowers of brimftone. Sulphur is alfo found in abundance in coal mines, and in the ores of different metals. In this ftate it bears the name of pyrites and the copper and iron pyrites are the fource of moll of the fulphur ufed in this country. In roafting the orfcs to obtain the metals, much fulphur is fublimed and collected. In other cafes the pyrites are piled in the form of pyramids, the fides of which are earthed up. By the addition of a fmall quantity of fuel the pile is lighted, and made to burn flowly, during which the fulphur is volatilized, and efcaping to the top, is SULPHUR, OR BRIMSTONE. 165 - there condenfed, and then melted in cavities deftined to receive it. When fulphur is burnt, it combines with oxy- gen, and forms fulphuric acid, or oil of vitriol. In the manufacturing of this acid,' about one eighth of fait pet re is added to the fulphur,. to affift the combuition, by affording oxygen. The operation is performed in chambers lined with lead, and the acid vapours are condenfed againft the fides, or abforbed by water, with which the floor of the chamber is covered. When this water is fufficiently impregnated, it is concentrated in leaden boilers, and rectified in glafs retorts, to render it white and pure. Sulphuric acid is much ufed by the dyers, and in a lefs oxygenated or acidified flate, when it is called fulphureous acid, it is ufed to bleach or whiten filk. When a match is lighted, and a rofe held over the vapours, its colour foon lades, and the rofe becomes white. This is effected by the fulphureous acid vapours that are formed, and proves its bleaching dualities. i. Sulphur united to the alkaline, falts forms the different hepars, or livers of fulphur. Acids decom pofe thefe, and at the fame time difengage a very offenfive gas, which is inflammable air, holding fulphur in folution. The SULPHURATED HYDROGEN GAS gives 166 SULPHUR, OR BRIMSTONE. the peculiar fmell and tafte to Harrowgate water. It is like that of rotten eggs, or the fcourings of a gun-barrel. Notwithftanding this peculiar, and, to raoft people, very difagreeable flavour, Harrowgate water is foon drunk without difguft, the palate being by habit foon reconciled to it. It tarnifhes filver, and blackens white paint. Charafters written on paper with a folution of fugar of lead in water, are made vifible, and rendered almofl black, by holding the paper over frefh Harrowgate water ; and ftill more readily byimmerfing it in the water. This has been had recourfe to for fecret correfpondence, for the characters are quite invifible before the applica- tion of the water. Many curious tales are circulated about ladies who have ufed white paint, being disfigured by bathing in thefe waters. The paint being a calx of lead (white lead) is immediately blackened by the appli- cation of the water. Sulphur feems to be afforded by animal and vege- table putrefaftion. 167 ESSAY XVI. THE ALKALIES. - 'i ’-h M! i . . () j > The alkalies are divided into volatile and fixed. Ammonia is the volatile, and foda and potafh are the two fixed alkalies. The latter are ftill confi- dered as elementary fubftances, although many cir- cumftances render it probable, that they are com- pounds of azote with one or other of the earths. Ammonia or the volatile alkali, it is now well as- certained, is a compound of azote (the bafe of im- pure air) and hydrogen (the bafe of inflammable air). Notwithftanding its being a compound, we fhall treat of ammonia, in this place, as allied in many of its properties to tlie fixed alkalies. Like them it changes vegetable blue colours to a green ; it ha* an acrid tafle ; renders oils foluble in water ; and when pure diffolves, or reduces to a jelly, wool and fonae other animal fubftances. Thefe may be confidered the general qualities of alkalies ; and now let us conflder each of thefe fubftances fepa- rately. Ammonia, or volatile alkali, in its pure flate, is in the form of gas ; when abforbed by water, it is the aqua ammonia puree, fometimes ufed in frnel- lihg-bottles ; and when rendered mild by its union 5 165 THE ALKALIES. with carbonic acid or fixed air, and cryftallized, it conftitutes the common fmelling falts. When equal parts of fal ammoniac (muriate of • ammonia) and quick lime, each in powder, are heated in a glafs retort, a gas is extricated, which, if colle&ed over mercury, retains its aeriform con- dition, and is the pure ammonia, or ammoniacal gas. If collefted in a veflel containing water, it is immediately abforbed, and conftitutes the aqua ammonia pur a, or liquid ammonia. The gas has a pungent fmell, turns red vegetable infufions to green, extinguifhes flame, and is fatal to animals. The chief *ufes of volatile alkali are as a medi- cine. It is produced by the putrefaction, or by the diftillation, of almoft all animal matter. It is this fait in a ftate of gas that gives the pungent fmell, and afifefts the eyes, on entering ftables, flaughter- boufes, and firnilar places, that are not well cleanfed. Sal ammoniac, from which the volatile alkali is chiefly procured, is a compound of ammonia and muriatic or marine acid; hence its name in the new nomenclature is muriate of ammonia . This com- pound fait is obtained by diftilling the foot, that arifes from burning the dung ot certain animals. It is moftly imported from Egypt, where the dung of the camel is dried in the fun, then burnt, and the foot carefully collected ; from which the fal THE ALKALIES, 169 ammoniac is procured by fimple diftillation. It is only the dung of fuch animals as feed on faline ve- getables, that will afford the fal ammoniac. There is nothing peculiar in that of the camel, as has been very generally believed. It depends folely on the kind of food ; and unlefs the animal has eaten the faline vegetables, fuch as grow on the fea fhore, and near to it, its dung will afford no ammoniac. There is a manufactory of fal ammoniac at Edin- burgh, but the procefs is kept a fecret. This fait is ufed in fome proceffes in the art of dyeing. It is ufed as a flux in foldering, and in fome cafes as a medicine. The fixed alkalies are of two kinds : the one called vegetable alkali, or potaih ; the other mineral alkali, or foda. They are both known in commerce under different names, according to the fubflances from which they are procured. Potash, or the vegetable alkali, is generally obtained from wood afhes ; but fometimes from the tartar, or from the lees of wine, in which cafe it is called fait of tartar . Mofl of our potafh is imported from the North, where wood is. in fufficient abun- dance to allow of its being burnt for this purpofe* The hard woods afford the molt fait ; but every vegetable, when burnt, affords fome. The allies are wafhed in water, which diffolves the potaih; the folution is then concentrated by boiling, and evaporating in iron boilers ; and the fait thus pro* I ft 0 THE ALKALIES. cured is fometimes heated in the fire to purify it from colouring matter. The vegetable alkali is ufed in bleaching, in making foap and glafs, and as a medicine. Wood aihes are frequently ufed in wafhing; in which it is the pctafh that proves ferviceable ; for by uniting with greafe, and other filth, it renders them foluble in water. For the fame reafon fait of tartar is fome- times ufed to take out greafe fpots. Soda, or the foflil alkali, is fometimes found in a native ftate, as in the lakes of Natron in Egypt, which are dry in the fummer feafon ; the water leaving, after evaporation, a bed of foda, or, as it is there called, natron, of two feet in thicknefs, which is dug out with iron crows, for fale. Such as is not obtained from this fource, is procured from the aihes of feaweeds, and certain plants that grow on the fealhore. Thefe vegetables are thrown to- gether in heaps, and burnt ; the afhes are then col- lected, and treated in the fame way as wood aihes for obtaining the vegetable alkali. When it is obtained from the feaweeds, as fea wrack, or tang, which are different fpecies of fucus, the fait is called kelp . When obtained from a plant called barilla, which grows in great perfection on the Spanifh coaft, the fait is alfo called barilla. There a*e feveral other vegetables which afford the mineral alkali ; as falfola kali , fome of the genus chenopodium , and alfo ibme of the atriplices . THE ALKALIES* f n The ufes of this alkali arc nearly the fame with thofe of the vegetable alkali, but it is more ufed in glafs-making. The alkalies, as we ufually meet with them, are in a mild hate, in confequence of their combination with carbonic acid, qr fixed air, which is the caufe of their effervefcing with acids. When boiled with quick lime, they lofe the fixed air, and be- come cauflic. The alkalies combine with ail the acids, and form neutral falts ; thus, when beer is four, a few grains of fait of tartar, or other vegetable alkali, added to a glafs of the beer, will neutralize the acid, and take off the tartnefs. The alkalies will all of them unite with oils, and the refult of fuch a combination is a soap ; the kind and quality of which depend upon the kind and quality, and alfo upon the proportion, of the ingredients. The firil part of the procefs confifts in making the alkali pure or cauflic by mixture with quick lime, which abflra&s from it the carbonic acid or fixed air. This cauflic lie, mixed with oil or tal- low in due proportion, and boiled to a proper con- fiflence, forms foap. Boil one part ot good barilla with two of quick lime in a fufficient quantity of water, flrain the li- quor through a cloth, and evaporate, till a phial, holding eight ounces of water, will hold eleven of I 2 THE ALKALIES* i?r this folution ; then boil one part of the lie with two of the oil 9 and you will have a good hard foap. In manufactories, where the fuel is of material confequence, the lie is made without boiling. Equal meafures of barilla and flaked quick lime are heaped up together, water is poured oil the top, and filtering through the heap is caught in proper vef- fels ; more water is then poured on, till no fait comes with it, and the lie of different flrengths is kept feparately. It is now mixed with the oil and tallow in boilers, the weakeft lie firft, then that that is ftrongef, and fo on } and when boiled fuffi- ciently the foap is made. The befit foft foap is made with five parts of pot- aflh, three of whale oil, and one of tallow. For foaps of an inferior quality, more tallow, kitchen greafe, or oil of an inferior quality, is ufed. And lately the French chymifts have recommend- ed a cheap foap to be made, by ufing woolen rags and old woollen clothes of all kinds, locks of wool, hair, and even the horns of animals, inffead of oil. Thefe fubftances are all foluble in the cauftic lie, atid by proper boiling form a foap. The chief in- convenience of fuch a foap is, that it poffeffes a very uripleafant fmell. It is however ufed by many of the cloth manufacturers in cleanfmg their fluffs; and as they require repeated waffling, the fmell is thereby completely taken off. 6 THE ALKALIES. 17 & The moll delicate foap is made with olive oil ; and a peculiar kind, called Starkey’s foap, is made by triturating ten parts of cauftic alkali hot, witlx eight parts of oil of turpentine, which inflantly forms a very hard foap. Another important ufe of the two fixed alkalies is in the manufacture of glass. Mixed with the (iliceous or flinty earth, they form a compound that is very fuflhle, and according to the ingredients more or lefs tranfparent ; and of fuch a mixture is glafs of every kind man u faff u red. The iiliceous earth is ufed either in the form of fand, of flint, of quartz, or fome other hard {tone of this genus. Such being felefted as is fitted: for the particular kind of glafs required. The common green bottle glafs is made of the common fand from the fea-fhore, for the filex, and the foap boiler’s refufe for the alkali. JBoth the ingredients therefore are impure, and confequently the glafs is of an ordinary quality. The alkali in the foap boiler’s refufe is calculated to aflifl the fufion of the mafs very confiderably, the quantity of filex renders it a very hard glafs, and it derives its green colour from a portion of iron, contained in the ingredients. The mafs is fufed in veflels made of Stourbridge clay, in a furnace of confiderable power, and the •bottles are lafhioned by blowing ; alter which they u 174 THE ALKALIES. are immediately put into the annealing oven, and allowed to cool gradually. Window-glass is generally made of a fine white fand, fuch as is found on the Norfolk coaft, and is called Lynn- fand, and the foda obtained from burn- ing the fea weeds, which is known by the name of kelp. The kelp is previoufly ^calcined to expel the fixed air. When the mafs is melted, it is run into large plates, and this operation is termed flafhing. The fame kind of fand is ufed for what is called flint glafs, but in this there is an addition of litharge, or fome other preparation of lead, which, befides promoting the fufion, makes the glafs to be more eafily cut, and alfo gives it a greater polilh. The flronger the heat required to fufe the mafs, in general the finer is the glafs ; and therefore when only a coarfe glafs is required, a greater quantity of flux is added. The addition of manganefe deftroys the colour, that would otherwife arife from the foreign ad- mixture of any inflammable matter ; and that too, in a great meafure, that arifes from iron. It is therefore always ufed, when a colourlefs and tranf- parent glafs is required. It is ufed for inftance in fine window glafs. When it is wilhed to gfve an artificial colour to glafs, different fubftances are employed for that THE ALKALIES. 175 purpofe. The blue colour, and various fhades of violet are given by the admixture of a metal, called Cobalt; and a fine green by fome preparation of iron. Quartz cryftal powdered, is ufed inflead of fand, in manufafturing a fine glafs for optical inflru- ments. Other kinds of filiceous earth are ufed in particular manufaftories, as being either more eafily procured, or more particularly adapted ta the kind of glafs there required* n 31 7 G ESSAY XVIL THE EARTHS. The frniple earths are nine in number ; but fe- \ r eral being newly difcovered, and by no means generally known, and little or not at all applied to ufeful purpofes, we fiiall merely mention the names by which they are defoliated, and pafs to the confideration of fuch as are more interesting. They are known by the following names: 1ft, lime; 2d, magnefia ; 3d, alumine ; 4th, filex ; 5th, barytes; 6th, ftrontian ; 7th, jargonia; 8th, g!u~ -cine; and, 9th, aguftine. The four firft are thofe that will be more particularly confidered. They are never found perfeftly pure, but always blended with each other, and often with other fub- ftances. Such earths and ftones however as confiflr chiefly* or owe their chief properties to any one of the fimple earths, are c Jaded together, and arranged as fpecies under that particular earth, as a genus. Thus we fiiall commence with confidering fome of the various forms under which lime is found, which is called the calcareous genus. Lime is found in moft countries, and frequently in great abundance* Like the alkalies it is cauftic, THE EARTHS. 177 when quite pure, but it is never found naturally in this (hue. It is generally combined with carbonic acid or fixed air, which renders it mild, and it is moftly mixed with fome of the other earths. The variety of forms, under which lime is found, may be divided into two claffes, the firft compre- bending thofe irregular maffes, that conflitute the calcareous ft rata, and fometimes form whole moun- tains, and the fecond including the calcareous cryftals, or fpars, that are regular in their figure, and found in confiderably lefs quantities. Both "kinds effervefce with acids, and are converted into quick -lime by burning. Of the firft clafs, chalk is the fofteft, and appa- rently of the lateft formation. It is found in large beds in many parts of this kingdom. When white and eafily pul verifiable, it is formed into what is called whiting. For this purpofe the chalk is agitated in water, to feparate the foreign fub fiances, as flints, pyrites, & c. ; the water is then poured off, and the chalk fuffered to fubfide ; which, when dried, is the whiting of the fhops. It has been obferved, that rooms newly white- wafhed are unwholefome ; and this has been ac- counted for, by fuppofing that the lime or chalk has the power of abforbing the pure part of The air. All the earths have been faid to po fiefs . this propei ty, but the fact is not yet decidedly aficer- tainedo The white-wafhing q£ apartments is ne» .15 m THE EARTHS. ceffary to cleanlinefs, and has been very properly recommended as part of the plan, for purifying hofpitals, and other buildings, from contagion; but if the preceding fuppofition be founded in fact, fuch rooms fhould not be ufed, till two or three days after the operation. In a hate harder than chalk, lime is known in Tome dihri&s under the name of clunch , which is burnt for lime, but is inferior for that purpofe to the more indurated fubhance called limejione. This is of various kinds, according to the hate of indu- ration, and the nature of the fubhances >vith which the lime is admixed. Some fpecies are fitteh for burning into quick-lime, and others for building. In general, the hardefi limehones afford the bell lime. In countries, where neither chalk nor limehone is found, fea-fhells, corals, and madrepores are col- lected from the fea fhore, and burnt for lime. When limehone is to be burnt, to expel the fixed air, and convert it into quick-lime, it is broken into fmall pieces, and placed on the kiln, with alternate layers of feme fuel, which is generally coal ; the fire is then lighted, and the mafs kept in a hate of ignition, till the air is all expelled, which may be known by its no longer effervefeing with acids. In this hate the lime is white or grayifh, it is cauhic, and has a great avidity for Water, by ap- plication of which it heats, burhs, and is reduced THE EARTHS. 179 to a fine powder. It is now called flaked lime, and when fifted, is fit for making mortar, which is done by working up with fan d, the fragments or daft of ftone, cmder-afhes, or fome fuch hard fub- ftance, and a fufficient quantity of water. Horfe* hair, or chopped hay or ftraw, are occafionally added, to make it, as the workmen term it, more binding. Quick -lime, whether alone or mixed up into mortar, has fo ftrong an attraction for carbonic acid, or fixed air, that, when expofed to the air, it gra- dually abforbs it from the atmofphere. Hence the neceflity of ufing lime,, for making mortar, as foon as it is burnt. It fee ms to be by this gradual con- verfion of lime into limeftone, that mortar hardens by age, and as it is a long time in acquiring its full quantity of fixed air, fo it is a long time before it has acquired its greateft degree of hardnefs. It is generally obferved, in pulling down very old build- ings, that the mortar is as hard as the ftone; and it has been inferred from thence, that the ancients poffeffed the art of making a much firmer cement, than what we ufe ; but it is very probable, that its fuperior hardnefs depends upon its having acquired more fixed air from the atmofphere. Another ftate, in which lime is found, is in ad- mixture with clay and fand, when it is denominated marl , which, as well as limeftone,. is very much ap- plied to the manuring of land. 16 180 THE EARTHS. Marl is called calcareous, argillaceous, or fandy marl, according to the proportion of lime, clay, or fand. The firft, or calcareous marl , is generally of a yellowifh white, or yellowifh gray colour, and h found a few feet under the foil on the fides of hills, or under turf in bogs. It is fomcthjies diflinguifhed by the name of (hell marl, when it abounds in the remains and fragments of fhells, and by that of {tone marl, when it is particularly hard and indurated. Argillaceous marl is gray or brown, or reddifh brown, or yellowifh, or blueifh gray. It is mofb unctuous or greafy to the feel, and harder than the former. Sandy marl is brownifh, gray, or lead coloured,, cmd contains fo much filiceous or flinty fand, that the refiduum, or what is left after pouring acid upon it, will not be duQile enough to form a brick, as is the cafe with the other marls. With refpedt to its utility in manuring land, a marl is not reckoned of any value, unlefs it con- tains thirty-five or forty per cent of lime. The eafieff mode of afcertaining which, is to immerfe a hundred parts of the marl, the value of which you wifh to afcertain, into a fufficient quantity of diluted muriatic acid. All that is diffolved by this means, is lime, and no more of it ; by weighing the re- mainder therefore* and fubtra&ing it from the THE EARTHS, IS! whole, you afcertain the e.xaft proportion, that a hundred parts of the marl contain. The laft form, in which the lime of this clafs is found, is in a hate of marble,. This is a lime- ftone capable of bearing a polifh; it is of different degrees of hardnefs, and of different colours. Its furface too is diverfified with veins, lines, fpots, and ether figures, differing in colour from the ground, and frequently containing the remains of (hells, and a variety of madrepores and corals. The ufe of marble, as the mod ornamental ftone for building, for fculpture, &c. is very .generally known. There is reafon foi believing, that moft lime-ftone rocks and ftrata, marbles, marles, and other calca- reous fubftances, have been originally formed by animals, and chiefly by marine animals, the exuviaa of which have been gradually collefled into thefe vaft: heaps, in which we now find them, and have by trituration and partial decompofition affumed their prefent appearance. A ftrong argument in favour of this opinion is deduced from the frequent appearance of (hells, -bones, and other -animal remains, in the different fpecies of calcareous ftones, particularly in chalks beds, and marble quarries. The (hells of the teftaceous animals confift wholly of carbonate of lime, or ehalk, with more or lefs annual matter, and that differently difpofed. THE EARTHS IM being in the porcellaneous fhells, as the cypraea, &c., in much fmaller proportion, than in the mother- of-pearl fhells, as oyfters, mufcles, &c. In the former, the animal matter feems to he uniformly difperfed through the calcareous matter, as a con- nefling medium. In the latter, it is membrana- ceous, and ftratified, being depofited bv the animal in alternate layers with the carbonate, fo that the membrane in thefe fhells retains its form after the calcareous matter is diffolved by an acid. The cruftaceous animals, as crabs, lobflers, fhrimps, and craw-fifh, have their fhells, confifling partly of carbonate of lime, and partly of phofphate of lime, refembling in this refpeCt the fhells of birds eggs. From this view we can eafily conceive, how the exuviae of thefe animals may form beds of chalk, and other calcareous flones, there being little more requiiite, than the decompofition of the animal matter. The fecond cla r s of calcareous produ&ions is, where the lime combined with fixed air, or with fome other acid, aifumes a cryflallized form, in- which cafe it is generally called spar. With the carbonic acid it forms the dog-tooth fpar, the columnar or pyramidal calcareous fpar, according to the fhape it afTumes ; and, when tranf- parent, it poflefTes t' e property of double refrv&iOJ* as the Iceland cryftah TAZ EARTHS. When combined with a peculiar acid, termed the fluoric acid, it forms Derby Chi re fpar, or blue John, as the miners call it, a flone much ufed for orna- ments. It is various, and often beautiful, in its appearance, and bears an excellent polifh. In ornaments of this kind, it is a practice, frequently had recourfe to by the workmen, to fill up the accidental cracks and flaws with an ore of lead, or of copper, which they execute very neatly, even fo. as to enhance the value of them, deceiv- ing the purchafer with the aflurance that it is na- tural. Lime, combined with fulphuric acid, is called gypsum, plalter of Paris, plafler hone* or fe- lenite. It is very abundant in fome countries. The hills near Paris are chiefly compofed of it, and in fome parts of America it is ufed as a manure, chiefly as a top dreffing to grafs land. When burnt or calcined, it is mifcible with water, forming a liquid, which, from its fuddenly drying, and be- coming folid, is much ufed for caking ornaments, as bufts, &c. In Derbyfhire, and the neighbouring counties, the plafler flone is much ufed for flooring. For this purpofe it is firft calcined, and then pow- dered. The powder being mixed with water to the proper confidence, is fpread to the required thick- nefs upon reed, when it immediately becomes folid. 184 THE EARTHS* It is this felenite, or gypfum, that generally gives to water the quality called hardnefs. Such water curdles foap, and is therefore unfit to wafh with. The fulphuric acid of the felenite attaches itfelf to the alkali of the foap, whilft the oil and lime are feparated in flakes, and give the appearance of curdling. It is a common practice to add wood-afhes to hard water when it is required to ufe it for wafhing; in this cafe the alkali of the wood-afhes xlecompofes the felenite. Hard water almoft always contains carbonate of lime or chalk, as well as felenite. By boiling the water this is feparated, and forms the iur or cruft on the infide of tea-kettles ; fo that hard water is ren- dered fomewhat fofter by boiling, though not quite To. For chymical purpofes this property may be wholly obviated, by adding to the water a fmall quantity of barytic folution. Pease, and other greens, retain their colour better when boiled in hard, than when boiled in foft water; but they are not fo foft and tender. Soft water is beft adapted to molt manufactures, as brew- ing, dyeing, &c. In dyeing, if hard water is ufed, the felenite, or its earthy part, is depofited in the fluff, and prevents the colouring particles from penetrating. In brewing, or any other procefs where water is ufed to extraft the virtues from vegetable, or from animal matter, foft water is THE EARTHS. IS* beft, becaufe its folvent powers are greateft. In making tea, hard water will not extraft fo much as foft, unlefs the tea be powdered; for it has not fo much the power of foftening and opening the tea leaves. Lime being evidently an animal fecretion, it has become a matter of difpute, whether it is abfo- lutely formed by animals, or only feparated from the food, and depofited in the form of fhells or bones in particular fituations. If it could be proved that all the lime jcontained in the fhell of the lobfter, or in the fhells or bbnes of any other animal, has not been received by the ftomach with its food, it muft follow, that lime is a compound,, not a fimple fub~ fiance ; whereas the chymilt has not yet been able to dete£l its conhituent parts. It appears, however, probable from feveral fafts, that the lime.. is received into the fiomach, and not formed by the animal. Lor inftance, chickens fed purpofely, and with great care, on fuch food as contains leaft lime, compared with others fed in the nfual way, were much more feeble, and their bones both fmaller and more flexible* Hens, alfo, kept carefully from lime, laid eggs without fhells; but on being allowed again to pick up pieces of lime, mortar, and the like, they laid eggs covered with their natural fhells. Mofl articles of food contain lime in fmall quantity. The faireli •experiments might be made by keeping fifhes .in 186 . THE EARTHS. diftilled water, as free from animalcula as poffible, either in the water or the furrounding air. Such fifhes we know will live and grow with no other aliment than air and water; and if the quantity of lime in their bones, fcales, and other parts, is found to be at the fame time increafed, it would amount to a proof that the fifhes have formed the lime, and, confequently, that lime is a compound. Such experiments require to be conduced with the greateft accuracy and attention to become fatis- faftory. Magnesia is an earth that is much lefs fre- quently met with than lime, and is never found alone. The ftones in which it conflitutes a con- fiderable part, are known by a peculiar greafy feel, as the French chalk (a fleatite), which is ufed to take greafe fpots out of filk ; lapis ollaris , a blueifh ftone, fo foft as to be eafily cut and fafhioned by a turning machine into a variety of utenfils; and laftly ajbcjlas , a fibrous flone, that may be fpun and woven into cloth. In fuch a cloth, which is perfeftly incombuftible, did the Romans fometimes burn their dead bodies, to preferve their afhes. Epfom fait is a combination of magnefia with fulphuric acid, and is found in a variety of natural waters. By adding an alkali to a folution of this fait in water, the magnefia is precipitated in a pure fiate, forming a white impalpable powder* THE EARTHS. 1ST Alumine, argil, or clay, is the next earth to be confiderech From its duflility when moiflened, and its hardening in the fire, it is made the bafis of bricks, tiles, and every kind of pottery or earth- enware. It is found of various degrees of purity, and mixed with a variety of other earths; fuch, therefore, are felefted by the manufacturers as are fitted for the purpofe required; and for the nicer kinds of wares, artificial mixtures oi clay and other earths are ufed. A tolerably pure white clay is ufed for making pipes. A fliff blueifh or grayifh clay, with a greafy feel, is fitted for bricks and tiles, which being naturally coloured with an iron ore, turns red by burning. To make bricks, the clay being dug, and thrown into heaps, is moiflened with water, and worked by men treading it down with their feet. It is then cut again with wooden fpades, thrown into heaps, and, if required, again worked with the feet. It is now carried to the brick-maker, who cuts off enough for a fingle brick, kneads it like dough, on a board fprinkled with land ; he then puts it into a wooden mould, previoufly moiflened, and levels it at top. A boy then turns it out upon the ground, where it remains till it is dry, being occafionally turned. The bricks are then piled up into walls, and expoied to the air, but fheltered from the 188 THE EARTHS* rain, and after a few weeks are put into the kiln& and burnt. For pantiles, the fame clay is ufed ; but it is kneaded or worked very fine, generally by means of a mill contrived for the purpofe. The common ftone ware is made by mixing a certain proportion of fand with the clay ; and the white or Staffordfhire ftone ware, by mixing pipe clay and powdered flint in different proportions* The clay is well worked in water, to feparate the Tandy parts ; and the fluid mafs, containing the purer parts of the clay, is then paffed through .fieves. The flints are calcined and then ground, by means of a very hard ftone called chert ; being then fifted into water, this fluid mafs is mixed with the fluid clay, and left to fet. The mixture, after being dried in a kiln, is tempered till fit for turning, and in this ftate is ufed for a variety of wares. The fineft: China-ware is formed by an admix- ture of what is called petunze, with clay. This- petunze is a granite partly decompofed, found at the bottoms of certain mountains, and properly prepared. Thefe mixtures are made into a duftile mafs with water, are well kneaded, and then fafhioned by a tinning machine or lathe, to the proper ffiape, and, ^ Jaftly, baked in ovens or furnaces, heated to the de- gree fuitabie to the particular article. THE EARTHS. ISO The coarfer kinds of pottery would be pervious to water were they not glazed, which is generally done with what is called potter’s lead ore, or fome other calx of lead ; or, if a black glazing is required, with a mixture of white lead, and an ore called manganefe. The glazing material is powdered and mixed with water, into which the veffels, previ- oufiy dried by a flight baking, are dipped. The po- rous veffel abforbs the water, and leaves the pow- dered ore on the furface, which, by expofure to heat in the oven, vitrifies and forms the glazing. The finer kinds of pottery, as the Staffordfhire ware, are glazed with common fait, which, being vaporized by the heat of the oven, unites with the clay, and vitrifies the furface, and in fome cafes, as with Queen’s-ware, the glazing is a mixture of white lead, powdered flint, and flint glafs. Other kinds become femivitrified in baking without any addition, in confequence' of the filiceous earth which they contain in their composition. The glazing material of Delft-ware is glafs ren- dered opaque'by an addition of oxyde, or calx of tin* In the manufa&ure of China and ^porcelain, after a firft baking they apply the glaze, then bake to vitrify this, next paint it, and, laftiy, bake again, to combine or amalgamate the paint with the glaze. For this kind of painting the colours are all pre- pared from metallic fubitances, as bell adapted to bear heat, and unite with the enamel in the laft bak- 190 THE EARTHS. ing, which they call burning in, or fixing the colours. Gold gives a beautiful purple ; iron a red ; lead, antimony, and filver, yellows ; copper, green ; cobalt, blue; and manganefe, a violet coloured paint. Queen’s- ware, the name firft given to the pottery made by Wedgwood, and called often Wedgwood- ware, is fuperior to molt others, being at the fame time cheap and ornamental, and pofTefling the valu- able properties of refilling the corroding effefts of acids, and bearing a very great degree of heat. Befides the very important ufes of clay, juft mentioned, it ferves another as important, namely, the manuring of particular foils. How the clay is to be felefted for this purpofe, and to what kind of foils applied, I fhall defer mentioning for the prefent, as I intend to treat prefently of manures in general. We fhal! conclude the confiaeration of clay, or alumine, with an account of the manufacture of alum. Alum is a mixture of fulphate of clay and fulphate of potafh ; it confifts, therefore, of fulphur acidified by oxygen, and combined, in the ftate of an acid, partly with clay and partly with potafti. It is chiefly manufactured from a flaty fubftance, called (hale, or aluminous fchiftus, which contains both clay and fulphur. This fchiftus is fometimes inflammable enough to burn by itfelf ; but when this is not the cafe, feme kind qi fuel is added to it, THE EARTHS. 191 and the fire kept up fome time. The fulphur. thus becomes acidified, and unites with the clay, forming an efflorefcence on the furface of the fchiftus. This is elutriated by pouring water on the heaps ; and, when faturated, this water is put into leaden boilers, and evaporated. During the evaporation, potafh is added to faturate the acid, which is ufually predo- minant, and likewife to affifl, which it effentially does, the cryfiallization of the alum. The lixivium, reduced to a proper flrength, is put into coolers, and the alum is cryflallized as the liquor cools. The principal ufe of alum is, as a mordant or fixer of colours in dyeing and in printing on cottons. It is alfo ufed in the preparation of leather. It is added to tallow, to render it harder for the making of candles. Mixed with glue, it in a great meafure prevents the depredation of infects on furniture. And the printers rub their balls with calcined alum, to' make them take the ink more readily.. Si lex, or filica, the laH of the fimple earths that I fhall mention, differs from all others, in being much harder, and infoluble in acids. Moll Hones, that are hard enough to ftrike fire with Heel, are of the filiceous genus. Flints, quartz, rock-cryfial, and the precious Hones, are all of this kind. The filiceous. earth becomes eafily fufible by addition of an alkali, and is therefore, as we before mentioned, the principal ingredient in glafs. Sands of different kinds, which are the filiceous Hones m THE EARTH So broken down by expofure to the weather, to water, and to accidents, and wafhed away by the waters, to be depofited in beds or hrata, are preferred in the manufa&ure of glafs, becaufe they are already in powder, and therefore fit for mixing with the other ingredients. The fnnple earths, we have faid before, are feldom found alone, but generally combined with each other, forming, however, an uniform rnafs, in confequence of their being intimately blended. In this hate they are denominated hones (imply, as limeftone, quartz, flint, afbehos, talc, garnet, &c. But frequently thefe hones are mixed, feveral of them together, into an irregular inafs, connected by a common cement, and in this cafe they are termed aggregate hones, as the granite, porphyry, pudding- hone, &c. Thefe conhitute what are called the primary mountains, wfailh the limehone mountains, chalk-hills, and hrata of land-hone, are termed fecondary, being fuppofed to be of later formation. As conneQed with the earths, we fhall now take into confideration the fubjeft of manures, and give a flight defeription of the different kinds of foils. 19J ESSAY XVIII. EARTHS, SOILS, AND MANURES. The confideration of the Ample earths leads us naturally to that of foils, which confift of thefe Ample earths in different proportions; and, as in- timately connected with this, we fhall at the fame time treat of the different fubftances employed as manures, and endeavour to afcertain the bell rules for adapting the latter to the former. The chief part that foils aft in the growth of plants, is to fupport the vegetable by its roots with fufficient firmnefs, and to fupply it with a proper quantity of water ; befides which, it fhould contain charcoal, or coaly matter, and certain falls in fmall proportion. From this it appears, that a good foil fhould be fufficiently porous, to allow the roots to ftrike freely, and to fuffer the fuperfluous water to drain off ; but, at the fame time, clofe and compaft enough, to retain the roots firm, and prevent the water 'draining off too faff. This is only to be obtained by a mixture of lime, clay, and filex or fand in due proportion ; for thefe earths retain the water in very different degrees, and form foils of K 1 94 SOILS AN© MANURES. very different degrees of compadtnefs, according to their proportions. The foils, moll frequently met with, are clay, chalk, fand or gravel, clayey loam, chalky loam, fandy loam, gravelly loam, ferrugineous loam, and boggy or heathy foil, or, as it is often called, mountain foil. Clay* is of very different colours, white, gray, brownifh red, brownifh black, yellow or bluifh. It feels fmooth, and fomewhat un&uous ; if moift, it adheres to the fingers, and is duftile. If thrown into water, it gradually diffufes itfelf through it, and then (lowly fubfides. Ufually it does not effervefce with acids, unlefs a firong heat be applied. If heated, it hardens, contrails in all its dimenfions, and, if fufficiently heated, forms bricks. It con- fills of alumine (pure clay) and fand, with a fmall proportion of calx of iron, which gives it its colour. The proportion of pure clay varies from twenty to feventy-five per cent, and is feparable from the fand, by boiling in firong vitriolic or fulphuric acid. Chalk, if tolerably pure, is of a white colour, moderate confiftence, and dufiy furface ; ftains the fingers, adheres (lightly to the tongue, and does not harden, but burns to lime, when heated ; lofing at the fame time four tenths of its weight. It effer- * By clay in this place I do not mean argil, or alumine, the Simple earth, but clayey foil, which is a compound of different earths, among which alumine is moll predominant. SOILS AND MANURES 195 vcfces with acids, and is diffolved almoft entirely thereih. By sand is meant fmali loofe grains of great hardnefs, not cohering when wet. It is generally filiceous, and therefore infoluble in acids. Gravel differs from fand chiefly in the fize of its particles ; but calcareous flones, when fmali and rounded, are often comprehended under the fame term. Loam denotes any foil moderately cohefive, that is, lefs fo than clay, but more fo than loofe chalk, and confills of clay and fand, with feme- times chalk. Clayey loam is that in which clay predominates, and is by farmers generally called ftrong, fluff, cold and heavy loam. Chalky loam is a mixture of clay, fand and chalk, the latter being in greater propor- tion, than it is ever found in clayey loam. It is alfo lefs cohefive than clayey loam. Sandy loam , in which fand, partly coarfe and partly fine, forms from eighty to ninety per cent, is lefs coherent than either. Gravelly loam differs from the lafl, in con- taining coarfer fand, and pebbles. This, with the two lafl foils, are termed by the farmers, light and hungry foils. Ferrugineous loam , or till, is of a dark brown, or reddifh colour, much harder and heavier than the other loams. It confifls of clay and the calces of iron more or lefs intimately mixed. Boggy soil confifls chiefly of ligneous par- ticles, being the roots of decayed vegetables mixed K 2 196 SOILS AND MANURES. with argillaceous earth and fand, and a coaly fub- ftance derived from decayed vegetables. H k'athy soil is that which is naturally pro- ductive of heath. Of the various foils, which we have now de- ferred, fome are much better adapted to fupport vegetation than others. Some are too fliff and retentive of water, others too loofe and too little retentive. Whatever will meliorate the foil in thefe particulars, is called a manure ; and diffe- rent foils, . of courfe, require different manures. Thofe fubftanccs, too, that improve the foil by fupplying coaly matter, and certain falts, as dung and compofts of every kind, are termed manures ; but as all foils require this kind of manure, when exhaufted of thofe principles, 1 fhall confine my observations to manures of the firft clafs, which aft chiefly in a mechanical way. I may however firft obferve, that paring and burning the land improves the foil, by reducing to afhes the old roots, and thus affording the fame nutriment to frefh vegetables, as is fuppiied by dung or other compoft. Burnt gypfum and quick lime anfwer the fame end, by aiding the putre- faftion of the old grafs, and dead vegetables. Our firft objeft mu ft be to afcertain in what particular any foil is deficient, and the next to difeover a manure that abounds in the particular earth required. a 197' SOILS AND MANURES.' 1 o afccrtain piecifely the compofition of a foil, requires a great deal of chymical knowledge; but lor common purpofes a fufficient degree of accu- racy will be obtained, by attending to the clifcri- minating qualities of the 'different foils, that I have given in deftribing 'them. The chief fubftances employed as manures are chalk, lime, clay, fand, marl, and gypfurn; all of which I have defcribed in a former effay. The particular earth in which each abounds, as well as the properties by which they are diftinguilhed, may be learned by attending to that defcription. The fituation of the land will make fome dif- ference in the proportions of the different earths requifite to form a fertile foil. On a declivity, for inftance, the foil requires more clay than on a plain. In a very rainy country, again, a lighter and more fandy foil is neceffary, than where there is lets rain. In the rainy climate of Turin, the moll fertile foil has from feventy-feven to eighty per cent of filiceous earth, and from nine to four- teen of calcareous ; whereas in the neighbourhood of Paris, where there is much lefs rain, the filex bears only the proportion of from forty-fix to fifty- one per cent in the moil fertile parts. The following obfervations will ferve as general rules for the adaptation of manures to the foils. Clayey foils require calcareous earth for a manure, and in that fcrm that i; beft fitted for opening the K 3 198 SOILS AND MANURES. texture of the foil, and making it lefs retentive ot moifture* For this purpofe nothing anfwers 10 well as marles ; and of thefe a gravelly marl, or as it is called by fome limeftone gravel, which is a marl mixed with lumps of limeftone, is the beft. Calca- reous marl is next in goodnefs ; next the filiceous ; and, laftly, the argillaceous. Where thefe manures cannot be had, a mixture of coarfe fand with lime or chalk ; and, if thefe are not to be procured, coal- afhcs, chips of wood, burnt clay, coarfe brick-duft, gravel, or even pebbles, will prove ufeful. Clayey loams may be defective either in the calca- reous ingredient or the fandy, or in’both. If in the firft, the proper manure is chalk ; if in the fecond, fand ; and if in both, filiceous marl, limeftone gravel, or mild lime and fand. There is a limeftone, found in Yorkftiire and fome other counties, called by the farmers hot lime, which, if ufed in the fame quantities with common lime, is very injurious to vegetation. It has been lately examined, and found to contain a large proportion of magnefia. This magnefan limeftone is eafilv diftins;uifhed from that which is purely calcareous, by being much more {lowly diffolved in acids, even the fofteft kind being much longer in di Solving than marble. A chalky foil wants both clay and fand, or gra- vel, therefore the beft manure for it is a clayey or fandy loam ; but when the chalk is fo hard, and fo SOILS AND MANURES. 199 difficultly reducible to powder, as to keep the foil fufficiently open of itfelf, then clay is the belt manure. Chalky loams , or light limeftone foils, which do not differ from them effentially, require clay or argillaceous marl. The beft manure for fandy foils is calcareous marl ; the next befl is argillaceous marl ; and next to thefe clay mixed with lime, or calcareous or argillaceous loams. Lime or chalk are lefs proper, as they do not give fufficient coherence to the foil ; but, when mixed with earth or dung, they anfwer very well. Sandy loams are moft benefited by calcareous or argillaceous marls, or by chalk for a firft, and clay for a fecond dreffing. Boggy foils , after draining, generally require burning ; and, as they are moftly clayey, they fhould have limeftone gravel, or lime mixed with coarfe land ; but if, as fometimes happens, they are fandy, lime or calcareous marl may be required. The above are to be confidered only as general rules; and as the foils partake more or lefs of the nature of thofe deferibed, the manures muft be fele&ed that correfpond more or lefs with thofe recommended. K 4 THE METALS. All the metals are fimple Jubilances. Accord- ing to the lateft difcoveries, tliere are twenty-one diftinfl metals. Their names are as follows : 1. pla- tina; 2. gold; 3 . filver; 4. quickfilver; 5 . copper; 6. iron; 7. lead; 8. tfn; 9 , zinc ; 10. antimony; 11. bifmuth ; 12. cobalt ; 13. nickel; 14. manga- nefe; 15. uranite ; 16. fylvanite ; 17. titanite ; 18. chrome; 19. arfenic ; 20. molybdenite; 51. tungftenite. Metals are diftinguifhed from other fubfiances by their great fpecific gravity, by their brilliancy, and by being more or lefs ductile or malleable. In this latter property, however, they differ confider- ably ; and thofe which poffefs it in the greateft de- gree are termed metals, whilft the others are called femimetals. Platiria, gold, and filver, undergoing no oxydation or calcination in our furnaces, are called perfect or noble metals, and the others 1 m- perfeft or bafe. Previoufly to noticing fuch interefting circurm Itances refpefting particular metals, as I have fe- le£led for this effay, I ihall make fome few obferva- THE METALS. 501 dons upon the ores of metals in general, as they are difcovered in the mines. Metals are found in four different conditions. lft. They are fometimes found in their metallic ftate, either pure and alone, or alloyed with other metals; in which hate they are called native. Gold is generally found in this condition ; filver, mer- cury, copper, and cobalt, not unfrequently ; and now and then iron, tin, and lead. In this ftate they only require pounding, wafliing, and then fufing or melting. 5dly. They are found mixed with fulphur, and fometimes arfenic, when they are faid to be mine- ralized. In this ftate they are brittle, and have not always the metallic luftre. Thefe ores are ufi\ally called pyrites, of which the iron pyrites are by far the moft common. Metals thus mineralized, after being broken dowfi^ or pounded, are feparated from the mineralizer by torrefaction, orroafting; the heat driving off the fulphur or arfenic. Sdly. Metals are found in a ftate of calx or oxyde, that is, combined with pure air or oxygen*- and moftly with a proportion of carbonic acid.- Thefe ores are triable, have an earthy appearance^ have different colours according to the degree of oxydation, and have no luftre. • They are reducible to the metallic ftate by heat r alone, or with the addition of charcoal. Iron, cop- K 5 20 2 THE METALS. per, tin, lead, and fome others, are occafionally met with in this date. 4thly. They are found combined with fome of the acids, in which cafe they are often regularly crydallized. When combined with the vitriolic or fuiphuric acid, they are termed vitriols ; as green vitriol or vitriol of iron (fulphate of iron) ; blue vitriol or vitriol of copper (fulphate of cop- per;) and white vitriol or vitriol of zinc (fulphate of zinc). In one or other of thefe dates now defcribed are the metals found, principally in the crevices of rocks, and they are called ores. Sometimes they are found in fands and the beds of rivers, as gold in its native date ; and frequently the metallic falts .are found in natural waters, which are then called mineral waters. The ores, filling up the crevices in rocks and mountains, are termed veins. Thefe veins fome- times contain nothing but the ore, but more fre- quently it is mixed in a confufed manner with fome earthy or dony fubdance, generally of the filiceous clafs, and this is called the matrix. The ore is extrafred with iron crows, or other implements ; and recourfe is frequently had to gun- powder, to feparate pieces of the rock, and make way for the working of the veins of ore. The working of mines is now become quite an art. The mode of doing it, depends upon the the metals. 203 fituation and dire6lion of the vein, the nature of the rock or mountain in which the vein runs, and feveral other circumftances, that none can appre- ciate but thofe that are in the habits of attending to fuch bufinefs. There are few circumftances that indicate the pre fence of a mine, and none that can be abfolutely depended upon. This, however, may be remem- bered, that granite rocks very feldom afford any, but that veins generally run in the fecondary moun- tains, as thofe of fchiftus, and fuch calcareous ftone as retains no impreffion of animals or vegetables. The prefence of a ftone called heavy fpar, too, is reckoned a favourable fign ; but the operation of boring can alone decide, whether our fufpicions refpefting the prefence of a mine are well or ill founded. Gold is found in its native ftate in the fands of many rivers, and particularly in thofe of South America. It is obtained by waffling fuch fand, and picking out the grains of gold ; or by powder- ing the earth or fand, and then adding quickfilver. The quickfilver will unite with other metals, but not with earths ; it is therefore intimately mixed with the earth or fa-nd, that contains gold or filver, and uniting itfelf to thofe metals affords an eafy means of feparating them from all impurities. The quickfilver is afterwards driven off by expofing the mixture to a ftrong heat. K G the metals. 20* Surprifing as it may appear, yet it is true, that gold exifts in a variety of vegetables, ,and may be obtained by a careful analyfis of their afhes, and likewife by that of vegetable mould. The quan- tity however is too minute to make it a profitable employment. This metal is fo very malleable, that one grain weight of it may be beaten out into gold leaf, fufficient tf> cover fifty-fix fquare inches. What is ufed for the coin of this kingdom is not pure, but alloyed with a certain proportion of copper. In the art of gilding upon copper, filver, brafs, &c., the gold is applied in a variety of ways, fome of which wc fhall defcribe. Iff. Hot gilding. In this the metal to be gilt is immerfed in, or wafhed with a folution of quickfilver in aqua fortis. This gives it a mercurial fur face, to which is afterwards to be applied an amalgam of gold, that is, a mixture of quickfilver and gold. The article being now ex- pofed to heat, the mercury flies off, leaving only a thin covering oi gold. If iron is the metal to be gilded, it muff be firft; immerfed in a folution of blue vitriol (fulphate of copper) %o acquire a furface of copper, which will receive the gilding, whereas iron itfelf will not. The colour of this kind of gilding is heightened by burning on it a covering of what is called gilder’s wax, which is formed of wax, verdigrife, and blue -Vitriol, It is laftly polifhed, and brightened with THE METALS. 205 a boiling folution of common fait and cream of tartar. The fecond mode is called the Grecian gilding of filver. A fait, called fal alembroth, which is a triple fait containing marine acid, ammonia, and 'mercury, is added to a folution of gold in aqua regia, which is a mixture of marine acid and aqua fortis, called aqua regia, from its property of dif- folving gold, which neither of them poffefTes fepa- rately This is evaporated to the confiftence of oil, and applied to the filver that is to be gilded. The third kind, called cold gilding , is performed by rubbing the metal with the allies of linen rags that have been impregnated with a folution of gold in aqua regia. Gobi wire is made by coating a filver rod with gold-leaf, and afterwards drawing it out into wire, which may be drawn fo fine that the covering of gold in fome places does not ex- ceed the fourteen millionth part of an inch. Silver is alloyed with copper, both for coinage, and for filverfmiths’ work, which renders it much more hard and durable. In the coinage of this country nearly one twelfth of copper is allowed. Any other metal may be filvered by rubbing it w T ith a paile made in the following way. DhTolve fine filver in aqua fortis, and then add as much tartar finely powdered as will make it into a paile. The modes employed for giving a furface of filver to other metals are very numerous. The plating of 203 THE METALS. copper is performed by fattening plates of {liver upon thicker plates of copper, and then rolling the two together into thin plates. The copper is gene- rally twelve times thicker than the Silver, and one ounce of filver is often thus rolled out to a furface of three fquare feet. What is called French plate is made by covering the copper, or more commonly brafs, with filver leaf when heated. Mercury, or quickfilver, which differs from all other metals in being fluid at the temperature of this climate, has however been frozen both by the natural cold of high northern latitudes, as at Kamtfchatka, and by artificial cold, produced by mixtures of fnow and aqua fortis. It is found to congeal at forty degrees below zero of Fahrenheit’s feale. Mercury unites with other metals, forming always a foft mafs, termed an amalgam. On this property depends the art of gilding, as above de- feribed, and alfo the art of coating looking-glaffes. To filver looking-glaffes in the ufual way, a sheet or leaf of tin foil, of the fize of the glafs, is fpread out upon a table; mercury is then poured upon it, and rubbed about with a brufn ; and more mercury poured on, till it covers the tin a full line in thick- nefs. The glcifs is now to be Aided upon it, preff- ing its edge clofe down, and along the tin. The glafs mutt then be very equally preffed with weights, and allowed to remain fo for two or three days. THE METALS, 207 For convex and concave mirrors, which cannot be fo preffed, an amalgam is ufed that is formed of two parts of mercury, one of tin, one of lead, and one of bifmuth. Mercury, when combined with fulphtir, is called cinnabar, whether it is a natural or artificial com- bination ; and the belt cinnabar, when finely levi- gated, forms the beautiful paint called vermilion. It is ufually in the form of cinnabar, that mer- cury is found in the mines ; but fometimes it is found pure in beds of calcareous earth or of clay. There are but few mines of quickfilver; the greateft quantity is procured from Spain. To feparate the mercury from the fulphur, quicklime or iron filings are added to the cinnabar to detain the fulphur, whilft the heat drives off the mercury. Copper is ufed in a variety of the arts. With tin it forms bell-metal and gun-metal, and with a metal called zinc it forms brafs ; or, if a lefs pro- portion of zinc is employed, an ornamental and ufeful compound, called Pinchbeck. Veffels made of copper for culinary purpofes are highly prejudicial ; for all acids, and all oily or fatty fubflances, when allowed to turn rancid, combine with the copper, and form verdigrife, which is poifonous, if taken in fufficient quantity, and very detrimental, even in the fmalleft quantities. Copper boilers mud confequently be highly im- proper ; for it is impofiible to keep them fo clean. &0* THE METALS. but that fome verdigrife will be formed about the edges, and unevenneffes, where the oily or fatty matters are fare to lodge. To prevent thefe bad effefls, moft copper veffels are tinned on their infides. To do this, the furface is well cleaned, by rubbing it either with fal am- moniac, or an acid ; the tin, or a compofition of tin and lead, or lead and pewter, is then melted in the veffel, and rubbed well about with old rags doubled up. But this tinning, let it be remem- bered, does not wholly prevent the bad effeCIs of the copper, as it foon wears off. It has been ufua'l to attribute the unpleafant cffecfs, often experienced from tea, to its being fomewhat impregnated with copper, from being dried on plates of that metal ; but it is now known, that iron plates, not copper ones, are employed for that purpofe. The ill effects of tea muff therefore be attributed to* its own properties, or perhaps in a great meafure to the debilitating power of hot water. Verdigrife for fale is mtfde by putting fheets of copper in alternate layers with a mixture of four wine and the refufe of grapes. After a certain time the plates are taken out, and placed edgewife in a cellar, where they are repeatedly fprinkled with four wine. The verdigrife, as it is formed on the furface of the copper, is feraped off, and packed up in leathern bags for the market-. THE METALS. £09 Blue vitriol, we have before faid, is a fulphate of copper. The common mode oi browning fowling- pieces is to wafh the barrels with a folution of this in water, by which a layer of copper is depofited, and this is lefs affe£led by the weather than iron. The fulphate of copper is ufed in dyeing, cryfials of verdigrife in painting, and copper itfelf in a variety of ways. Iron is chiefly found in the form of an oxyde, that is, combined with oxygen. It is diffufed more through different natural produ£lions than any other of the metals. It exifts in fmall proportion in moll animal and vegetable, as well as in moll mineral produftfons. According to the degree of oxyda- tion, it affumes different colours. It is the colour- ing fubllance of moll of the gems and precious Hones, of the different clays, and other earths, and of a variety of paints and pigments. From the variety of conditions, which it is capa- ble of affuming, according as it is mixed with more or lefs carbon, and oxygen, it is the moll ufeful of metals. It is the proportion and Hate of combination of thele fubllances with iron, that conflitutes the dif- ference between iron and Heel, between call iron and forged, iron, between red fhort iron and cold fhort iron, and between all thefe and plumbago or black lead. When combined with a certain pro- portion of carbon or charcoal it conllitutes Heel, 210 THE METALS. and with a much larger proportion it forms plum- bago ; for which lad, therefore, black lead, as it is generally called, is a very improper name. The ufes of iron in thefe various dates it is needlefs to mention. The plumbago is found mod abundantly in Cumberland. It is fawed into fmall flips, to form the black lead pencils ; but an inferior fort is made by mixing up the black lead dud into a pade. Iron combined with vitriolic acid forms green vitriol ; from which, when diffolved in water, the 1 iron is precipitated in form of a black powder, by adding to it any vegetable adringent, as galls, oak bark, or the like. On this depends the art of mak- ing inks, and black dyes. A- very good ink is made by the following proportion of ingredients. Nut-galls, one {)ound ; Gum arabic, \ r , r > or each fix ounces ; Green copperas, J Water four pints. The galls are- to be bruifed and fuffered to dand in the water (being now and then fliaken) for four hours. The gum is next to be added, and when this is diffolved, the copperas. The liquor imme- diately becomes black, in confequence of the pre- cipitation of the iron ; and the ufe of the gum is to fnfpend the black powder, which would otherwife fall to the bottom. Inkdains may be eafily taken out by any of the acids, either from cloth# paper, or THE METALS. *11 wood. Lemon juice is the bed, becaufe with it there is no danger of injuring the article. The acids will only take out writing ink, not printing ink, and therefore they may be ufed for cleaning books that have been defaced by writing. When ink-fpots have remained long, they be- come iron moulds, and are then taken out with more difficulty ; and the more fo, the longer they Hand, in confequence of the iron, by repeated moiftening and expofure to the air, having ac- quired fuch an addition of oxygen, as to make it infoluble in acids. To difeharge thefe old ftains, an alkaline fulphuret, or liver of fulphur, ffiould be firft applied in folution, and after this is w T ell w'affied off, the lemon juice or other acid ffiould be applied. As conneded with this, I ffiall here mention the belt mode of taking out fruit or wine ftains, and fpots of greafe or of wax. For the firft, put about a table fpoonful of marine acid (fpirit of fait) into a teacup, and add to it a tea fpoonful of powdered manganefe. Then fet this cup in a larger one filled with hot water. Moiften the ftained fpot with water, and expofe it \o the fumes, that arife from the teacup, till the ftain difappears. The tumes are thofe of the oxygenated muriatic acid ; but as they difeharge all printed and dyed colours, this mode is only applicable to white ar- ticles. THE METALS* £ I 2 Greafe-fpots arc moft effectually removed by a di- luted folutinn of pure potafb, or cauftic lie. Stains- of white wax are taken out by fpirit of turpentine, or fulphuric ether ; and the marks of white paint may likewife be removed by the laft mentioned fubilance. P/uflian blue, fo much admired as a pigment, is a combination of iron with a peculiar acid, called the Pruflic acid. It is obtained, by a complicated procefs, from blood and fome other animal produc- tions. I fhall conclude thefe few observations refpefting iron, with the procefs of making what are called tin plates ; for you muff know that thefe plates are not tin, but iron (lightly coated with tin. What are ufually called tin veffels, therefore, are iron, veffels, having the furface covered with tin ; and fuch only as Y orkfh i re Aghaloo, Ireland Afhwood, Ditto Afkeron, Yorkfhire Bilton, Ditto Broughton, Ditto Buglawton, Chefhire Cawley, Derbyfhire Chadlington, Oxfordfhire Codfalwood, Staffordlhire Crickle Spaw, Lancafhire Croft, Yorkfhire Cunley-houfe, Lancafhire DerrindafF, Ireland Derryhence, Ditto Derrylefler, Ditto Drumafnave, Ditto Drumgoon, Ditto Durham, near to Keddleftone, Derbyfhire Killafher, Ireland Liibeak, Ditto Maudefley, Lancafhire Meehan, Ireland Normanby, Yorkfhire Owen Breun, Ireland Laonfbury, Yorkfhire Pettigoe, Ireland Queen Camel, Somerfetfh. Shapmore, Weftmoreland Shettlewood, Derbyfhire Shipton, Yorkfnire Sutton-bog, Oxfordfhire Swadlingbar, Ireland Upminfter, EfTex Wardrew, Nor thumberland Wigglefworth, Yorkfhire (b) without purging Salts, Moffat , Scotland Carftarphin, Ditto Llandrindod, South Wales Nottingtcn, Dorfetfhire M 2 244 TABLE OF MINERAL WATERS. Division II. Hot. Aix la Chapelle, Germany Baden, Ditto Bareges, France Borfet, Germany Mont d’Or, France £4# ESSAY XXL ARTIFICIAL MINERAL WATERS. The natural mineral waters have been fo repeat- edly and ably fubmitted to chymical invelligation, that we poffefs now a very accurate analyfis of all that are important. This knowledge of their compofition has en- abled us to imitate moll of them, and thus to dif- fufe more generally the benefits that fucli waters afford. Thofe waters that contain only folid ingredients are very eafily imitated. Such as contain gafeous fubllances, require more contrivance, and fome of them are only to be exaftly imitated by very complex and intricate proceffes. This point, however, has been attained ; and the artificial waters of Paul, Scheppe, and of Mr. Wil- liam Henry of Manchefter, may be depended upon as very accurate imitations, and as poffeffing all th§ medical virtues of the natural waters. Thofe of the lalt gentleman I can more parti- cularly recommend from, my knowledge of his very intimate acquaintance with all chymical fub- jefts, and his wonted accuracy in experiment; and likewife from my knowing him to have laboured of M 3 £46 ARTIFICIAL MINERAL WATERS. late with peculiar affiduity in this particular branch of the fcience. Our acquaintance with the compofition and medical qualities of the natural waters gives us an opportunity of forming artificial ones, that differ from them in both particulars; and, by leaving out the more inert materials, to form Waters more fiinple than the natural ones, and yet poffefling the fame properties as medicines. It is only fuch as can be eafily made, that I* fhall here enumerate' and defcribe; and, for the fe, the only apparatus, that is required, is that in- vented by Dr. Nooth, and known by the name of Nooth’s apparatus for making the artificial mineral waters. Class I. Simple Waters. Should the cold fimple waters, as the Malvern , be required to be imitated, common rain water fhould be deprived of its chalk by boiling, and rendered ftill purer by diftillation. This water fhould then be expofed to the air, that it may abforb a portion of common ait", which boiling has deprived it of, and which the Malvern water always holds in folution. It will now only differ in holding perhaps more felenitethan Malvern water does; but this will be very trifling, if rain or fnow. water has been ufed. ARTIFICIAL MINERAL WATERS. 247 The fame water heated to 66° will referable Mat - lock, and heated to 82° Buxton water. To form Briftol water, impregnate diftilled water with fixed air,, by means of Nooth’s apparatus*, and add to a wine gallon feven grains of muri- ated magnefia, four of common fait, and eleven oi Glauber's fait. This imitation will be tolerably accurate, and when heated to 74° will poffefs the fame properties as the natural water when frelh drawn. To heat this and fimilar waters for drink, immerfc a bottle of it, well corked, into hot water, till it has acquired the proper heat, which may eafily be learnt after a few trials. Class II. Chalybeate zvaters. This is by far the moll extenfive clafs, and contains the greatell variety. To imitate the fimple cold carbonated chalybeates, fuch as that of Tunbridge , and a long lift of others that follow it in the preceding table, impregnate diftilled or even common pump water with fixed air, but not fo much as for the Briftol water, and fufpend a drachm of iron wire, or iron filings, in the middle veftel of the apparatus. The more fixed air is' ab forked by the water, and the longer it remains before it is drawn oft, the more iron it will dif * Vide Page 131. M 4 £48 ARTIFICIAL MINERAL WATERS* folve, and the more flrongly chalybeate it will prove. 1 he highly carbonated, as Spa , and Pyrmont , contain much more air and iron. To imitate the firft, ufe rain water, and for the latter a very hard water. To the firft, add nine grains of magnefia and three of foda to each quart; to the latter, one fcruple of magnefia, eleven grains of Epfom fait, and three of common fait, and allow them to abforb more of the fixed air than the common chalybeate*, particularly for the Pyrmont water. To imitate the Bath water precifely would be difficult, and perhaps in the prefent ftate of chy- miftry impoffible, as it contains the filiceous earth in folution, which is generally cordidered as infoluble. Common water very flightly impregnated with iron and fixed air (not fo much fo as to fparkle) when heated to 116° will not differ much in its medical qualities from Bath water. The /aline carbonated chalybeate waters may be pretty nearly imitated, as the Cheltenham and Scarborough, by adding more falts to the cpmmon chalybeates. To each quart, for the former, add a drachm of Glauber’s fait, and a drachm of * Epfom fait; and, to be more accurate, impreg- nate it very flightly with fulphureous ga*, as ARTIFICIAL MINERAL WATERS. 249 will be dire&ed prefently for the fulphureous waters. To imitate the Scarborough add only one third as much falts, ufe a harder water, and omit the fulphureous impregnation. The hot faline highly carbonated chalybeates, as Vichy and Carljbad , are imitated by impregnating water ftrongly with fix- ed air, fiightly with iron, and then adding to each pint, of Glauber’s fait two fcruples, common fait five grains, and mild foda 1 1 or 12 grains. The water is then to be heated to a fufficient tempera- ture for ufe ; the natural waters being too hot either for bathing or drinking when frefh drawn. The v it r iola ted chalybeates are imitated by adding more or lefs of green vitriol, and a fmall portion of alum, to common water. For an accurate imitation of the Hartfell wa- ter, firil impregnate a very pure water (lightly with iron and fixed air in the common way, and to a quart of this \vatcr add a fcruple of green vitriol, and three grains of alum. Class III. Saline waters , The fimple faline waters are imitated by adding fome oi the purging falts to a. tolerably pure water. 7 For artificial fea water , add half an ounce of common fait, and a drachm of muriate of magnefia, M 5 250 ARTIFICIAL MINERAL WATERS. to a pint of water. For Epfom water , diffolve a drachm of Epfom fait, and a few grains of muriate of magnefia, in each pint; and for Sedlitz water , add of Epfom fait five drachms, magnefia five grains, and of muriate of magnefia nine grains. Other falinfc waters contain small quantities of common fait wich the Epfom or Glauber’s fait, or both; but, as in virtues they are nearly if not altogether fimilar, it is rieedlefs to defcribe them. The highly carbonated alkaline 'waters are more difficult of imitation ; «• and whoever requires good Seltzer or foda water, had better apply to the noted venders of them, than attempt an imi- tation. To a pint of clear water, add five grains of magnefia, four grains of foda, and 17 grains of common fait ; then impregnate with as much fixed air as poflible, and the more air you make it im- bibe, the nearer will it be in quality to the Seltzer water. Class IV. Sulphureous waters . The fulphureous quality of thefe waters de- pends upon the prefence of inflammable air hold- fag fulphur in folution; and to impregnate water with this fulphurated, or hepatic gas,' the fame ap- paratus and fame procefs are required as for impreg- nating it with fixed air; with this difference, -that 1 ARTIFICIAL MINERAL WATERS. 251 liver of fulphur mull be fubflituted for chalk or marble. Liver of fulphur is made by mixing equal parts of fulphur and of potafh or quicklime, placing the mixture in an unglazed difh over a gentle fire, and ftirring it till it forms a uniform blood-red mafs. Some of the chalybeate waters are {lightly ful- phureous, as we before mentioned; to imitate which fome liver of fulphur mull be added to the chalk in the bottom velfel. To imitate the true Sulphureous wafer's , only liver of fulphur and the vitriolic acid are to be put into the bottom velfel ; and the necelfary falts, without iron, into the middle one. Moll of the fulphureous waters contain fo much faline matter as to prove purgative, of which Harrowgate water is the moll noted. To imitate this you mull add to each quart 2\ drachms of common fait, 22 grains of muriate of magnefia, and 2\ grains of Epfom fait. Of thofe fulphureous waters, that are not purga- tive, the Moffat water Hands, firlt; which is very nearly imitated by adding 8 grains of common fait to a quart ol the fulphurated water „ . The artificial fulphureous and chalybeate wa- ters, made according to the above direftions, cannot be expefted to be accurate imitations, becaufe it is difficult to appreciate the quantity M 6 252 ARTIFICIAL MINERAL WATERS. of fulphurated gas in the latter, or fixed air and iron in the former, that the water may have abforbed. They will however be found to poflefs the dif- tinguifhing properties, and perhaps all the medical virtues, of. the natural waters. ESSAY XXII. ON THE RED WELL AT WELLINGBOROUGH. Wellingborough is fuppofed by fome to be the fame with Wendlynburc, mentioned by Ingul- phus as one of the many towns deftroyed by the Danes ; but by others it is fuppofed to be a town of more modern date, deriving its name from the well, which we are about to treat of, the waters of which had formerly obtained very great celebrity for their medicinal virtues in the cure of a variety of complaints. Nearly two centuries ago it was in confiderable repute, being noticed' and recommend- ed by Sir Theodore Mayern, a writer of that time, and phyfician to King Charles the fiirft. It is likewife mentioned by Mr. John Goodyer, and by Dr. Merret ; and there is a tradition, confidered as tolerably authentic, that King Charles the Firfl and his Queen refided here in tents erefted on the hill, during a whole feafon, for the benefit of the water. Amongfl the inhabitants it has ftill retained confi- derable repute, and many of them have occafionally reforted to its water, and derived confiderable ad- vantages from the ufe of it. From thefe circumftances, from an accurate ana- lyfis of the water, and a comparifon of it with that ON THE RED WELL- 254 of Tunbridge, and other chalybeates, I believe it to be a water of confiderable virtues ; and I am in- duced to publifh this account of it in hopes that it will one day recover its wonted and deferved cele- brity. Wellingborough is a well built flourifhing mar- ket town in Northamptohfhire, {landing in a dry fituation on the fouth frde of a hill ; at the bottom of which, about a quarter of a tail e from the town, runs the river Nyne, a low hill or rifing ground in- tervening. • Shoemaking and lacemaking are the chief- em- ployments of its inhabitants, the number of whom by the late calculation appeared to be about three thoufand. The well or fpring, called Red well, is fituated in a hollow on the top of the hill, on the fouth fide of which the town is built. It. is north weft of the town, at the diftance of nearly half a mile. Its name is derived from the ochre or ruft of iron depofited in its courfe, which gives a rod appear- ance to the ftones, weeds, and other fubftances, over which the water runs. The quantity of water that the fpring affords is very confiderable at all feafons, fufficiently fo for all the purpofes it would be required for, were it as much reforted to as any ot our moil celebrated cha« lybeates. AT WELLINGBOROUGH. The water has been obferved to flow during ver y intcnfe frofts ; nor am I certain that it* has ever been known to be frozen. When frefh drawn the water is beautifully clear and transparent, but not fparkling like the Seltzer water. When drunk it has the peculiar inky fla- vour of all chalybeates, but not fo intenfely as to be difagreeable to the tafte. Its effefts are to quicken the pulfe, produce a general glow immediately after being drunk, and to prove gently aperient, more fo than mod chaly- beates ; befide which, it almoft univerfally in* creafes the quantity of urine. The continued ufe of the water increafes the ap- petite, exhilarates the Spirits, improves the ftrength, and braces the whole fyftem. Like all other chalybeates it blackens the faeces of perfons who drink it, which is a thing of no im- portance, but neceffary to be mentioned, and made known to the patient, left he take any groundless alarm. Examined with the proper chymical reagents this water appears to differ from Tunbridge water in no refpefts, except that of containing rather a larger proportion of earthy ingredients, chiefly chalk (car- bonat of lime), which being held- in folution by the fixed air is depofited on boiling, and alfo by mere expofure. The depofition of this matter forms a calcareous cruft intermixed with the ochre on the ON THE RED WELL fides and bottom of the bafin, into which the water flows. The other contents of the water are iron, fixed air, and a fmall quantity of purging falts. The chalybeate waters fometimes produce nau- fea and vomiting, or headach and dizzinefs, on be- ginning a courfe of them ; but thefe fymptoms ufu- ally go off in a few days, particularly if the water proves aperient, and increafes the flow of urine. The water very frequently purges pretty brijfkly at firft, but often after a long ufe produces a cof- tive habit of body. When this is the cafe aperient medicines fliould occafionally be taken. The difeafes, in which the ufe of the Red well water promifes to he. of moll fervice, are indigef- tion, with its various fymptoms, and a variety of complaints peculiar to the female fex . Of the latter, that debility and pallid countenance, liflleffnefs and averfion to every kind of exercife, fo frequent amongft the young, and particularly thofe of a delicate habit, are more fpeedily and cer- tainly removed by a courfe of thefe waters than, by any other means. Thefe waters may likewife be taken with great profpeft of advantage in all cafes of debility, and relaxation, from exceffive difcharges of any kind ; provided they be not attended with fever, or with local irritation, or pain. AT WELLINGBOROUGH. 257 Of ftoinach complaints, flatulency, an uncertain and capricious appetite, heartburn, and all the fymptoms attendant upon irregular and incomplete digeftion, are fuch as point out the ufe of this clafs of waters ; and whether they proceed from irregula- rity in diet ; habitual fmoking or chewing of to- bacco, which are not unfrequent caufes ; from long confinement, with want of air and exercife ; or from intenfe application, and continued inclina- tion of the body, as in writing, reading, and many of the employments of mechanics ; the continued ufe of this water with regular exercife and mental relaxation in different amufements, may be had re- courfe to with fanguine expectations of advantage. Patients that are low and hypochondriacal, lan- guid and inactive, with general relaxation and debi- lity, and all convalefcents from fevers, or other complaints, in whom the appetite is long in return- ing, may likewife expeft benefit from the ufe of chalybeate waters. The belt mode of taking the water is to begin early in the morning with a dofe of half a pint, then to walk or take other exercife for an hour, and after that to take another half pint, and to repeat the dofe a third time an hour or two before dinner. This plan fhould be continued daily for fix weeks or two months ; and, if the complaints are not by that time removed, after two or three months inter- ON THE RED WELL, &C. val a fecond courfe fhould be gone through in the fame way. There is no occafion for any preparation previ- ous to the ufe of the water, unlefs the ftomach is judged to be foul, and then a fingle emetic may precede its ufe. If the- body fhould be colli ve dur- ing the courfe, the water fhould occafionally be omitted for a day, and a gentle laxative medicine be given ; or a fmall quantity of fome purging fait may be daily added to the water* ESSAY XXIII. ON DYEING. The art of dyeing, confifls chiefly of cbymical proc^ffes, and comprifes a vail collection of chy~ inical experiments. To give a detailed account oi all the complicated operations of the dyc-houfe would be tedious, and uninterefting to any but the praftical dyer. Our intention is only to give the rationale of the art, and convey fuch general information, as fhall fatisfy the curiofity oi die general reader, but without qualifying him for the practical department of it. It is neceffary to preface the consideration of dyeing with fome observations on the fubftances,, that are to be Submitted to the operation. Wool,, hair, Silk, cotton, hemp, and flax, are what are principally fubje&ed to the dyer’s art. Of thefe the animal productions* namely, wool, hair, and {ilk, are more eafily dyed than the vege- table fubftances, cotton, hemp, and flax, becaufe they have a ftronger atti aCtion for the colouring particles of the various dyes employed. The animal fubftances are more eafily injured by acids and alkalies, which makes it neceffary^ to be more careful in the ufe of thefe, when dye- 260 ON DYEING. ing or preparing for the dye fuch fubftances, viz, wool, hair, and (ilk. Wool has a natural covering of greafe, which it is neceHary to deprive it of, before fubmitting it to the dye. This is done by fcouring it with warm water, to which is added one fourth of {tale chamber lie, and by afterwards wafhing it in a bream of clear water. The wool lofes a great deal in weight by this operation, often as much as one fifth of the whole. Befide this cleanfing it is generally neceflary to boil the wool in a fo- lution of alum and tartar, before it is dyed. This however is not requifite for all kinds of dyes ; and then it only needs, after the above cleanfing, to be wafhed in warm water, wrung out, and left to drain, which indeed is neceffary - with every Other fubftance that we intend to dye. Silk is naturally covered with a glairy varnifh, which is perfeftly foluble in water ; and the Eu- ropean filk has a yellow colour, which water alone will not deprive it of ; filk, therefore, is always fcoured with foap and water, previous to dyeing ; and to make it take and retain the colour, it is always alumed, which is done by wafhing it in a cold folution of alum in water. Cotton , which is a vegetable produftion, found enveloping the feeds of certain plants, has ufually in its natural bate a lighter or deeper tinge of yellow, of which it mud be deprived by bleach- ON DYEING. 2Gi ing. It mull then be fcoured in an alkaline lie, or in four water, which is prepared by mixing bran with water, and fuffering it to remain until it fer- ments, and becomes four. Afterwards, befides alumisg, as with filk, it requires to be wafhed in a deco&ion of galls, or other aftringent, as hot as the operator can well bear it. Linen , which is made either of flax or hemp, has always a brown colour, of which it mufl fc>e deprived, like cotton, by bleaching, and then undergoing the fame procefs as we have jull de- fcribed. In the art of dyeing there is a ftep, which is in almoft all cafes neceffary to be taken previous to immerfion of the ftuff into the dyeing liquor. This is the application of what is termed a mor - dant y the nature and intention of which I fhall now endeavour to explain. In moft cafes it is found neceffary to employ fomething for the purpofe of making the ftuff, to be dyed, take the- colour more readily, and re- tain it more firmly ; for by merely immerfing the fluffs into the dyeing liquor, they will feldom take a deep dye ; and the fluffs will in almoft every cafe lofe their colour again, by expofure to the air, or by wafhing in water. The fubftances thus employed, to give luftre and durability to the colours, are called mordant's . Different mordants are ufed for preparing dif. ON DYEING* <262 fercnt goods, and for preparing the fame for dif- ferent colouring drugs. Alum is by far the moll extenfively ufeful, being always employed in the printing of linens, and cottons, which is a fpecies of dyeing now very much praftifed. For the dyeing of filk and wool, metallic folutions are more fre- quently employed as mordants. The art of printing on cotton and linen depends chiefly on the application of the mordant. What is ufed for this purpofe is called the aluminous mor- dant, being prepared by diffolving three pounds of alum in a gallon of hot water, then adding a pound of fugar of lead, ftirring the mixture well at times for two or three days, and afterwards adding to it two ounces of potafh, and the fame quantity of chalk. The alum and fugar of lead in this preparation are both decompofed, the fulphuric acid of the alum uniting with the lead forms an infoluble powder, which therefore fubfides to the bottom, whilft the vinegar (which is the other conftituent of fugar of lead) combines with the clay or alumine of the alum, and remains diffolved in the fluid. This liquor then is not a folution of alum and fugar of lead in water, but a folution of acetite of alumine, that is, a fait compofed of vinegar and clay. This mordant, being thickened with ftarch or gum, is applied to the cloth by blocks* or by the ON DYEING. 2G3 pencil on thofe parts where the dye is afterwards intended to take, and give the pattern. It is then dried, and afterward wafhed, to get Out the gum or ftarch, and is now to be immerfed into the dyeing liquor. The pattern or part, to which the mordant was applied, has a much deeper tinge than the reft, when the fluff is taken out of the liquor ; and after the cloth has been repeatedly boiled in bran and water, and bleached in the air, this is the only part that retains the colour. The ufe of the mordant is explained, by flip- pofing that the particles of clay have a ftrong attraction for the particles of the colouring drug, and that having itfelf penetrated the cloth, it attrafts and retains there thefe colouring particles. To illuftrate this attra&ion or affinity, diffolve cochineal in a folution of alum, and then add an alkali, which will feparate the clay of the alum from its fulphuric acid, and caufe it to be precipitated. The clay, as it falls, attracts and carries with it to the bottom the colouring particles of the cochineal, the liquor above remaining clear and colourlefs. Solutions of different metallic falts are frequently employed as mordants, having a great affinity for the colouring matter of fome fubftances. They have a ftronger attraction for animal than for vege- table fluffs, and are therefore principally ufed in dyeing filk and wool. We now proceed to the confideration of the ON DYEING. colouring drugs, and the mode of employing them as dyes for different fubftances. Dr. Bancroft in treating this fubjeft has divided the colouring drugs into fubftantive and adje&ive, the former including fuch as may be permanently fixed in or upon the dyed fub fiance without the interpofition either of an earthy or metallic mordant, the latter including thofe which require the aid of a mordant. Others have divided this part of the fubjefl ac- cording to the kingdom of nature, which affords the dyes, treating feparately of the animal, vegetable, and mineral colouring drugs. The divifiom we (hall adopt, which is according to the colours they afford, though perhaps lefs fcientific, will be more congenial to our plan, as w r e mean to treat of the proceffes of dyeing, at the fame time that we particularize the fubftances that afford the colours. The three fimple colours are red, yellow, and blue; all other colours are compounded of thefe. Different (hades or tints pf the fame colour are produced by ufing different drugs, or by varying the quantity of colouring particles; or, in the cafe of the compound colours, by varying the propor- tion of the different fimple ones, of which they are compofed. Reds „ We (hall treat of the fimple colours find, and begin with red. Cochineal, kermes, and gum lac, among.fi the animal produ&ions ; and madder, 3 ON DYEING. £65 archil, carthamus, and Brazil wood, amongft the vegetables, are the chief fubftances employed as red dyes ; and as they differ in the tint and other pro- perties, as well as in the manner in which they are applied, we fhall fay a few words refpe&ing each. Cochineal is a finall infeft brought from Mexico, where it is found only on one plant, the caftus, or Indian fig. This is planted for the purpofe, and the growth of the infeft artificially encouraged. It is the principal fubflance now employed in dyeing the compound colour of fcarlet in confidering which, the b eft mode of ufmg cochineal will be mentioned. Kermes , a produclion very much of the fame nature with cochineal, gives a fine red dye to woollen goods, lefs vivid but more lafting than that from cochineal. It is not much ufed in the prefent day, but is feen frequently in old tapeftry, where it retains nearly its original luftre. Wool muft be prepared for this dye by boiling in water with one-fifth of its weight of alum, and half as much tartar, for two hours, and by being after- wards left in the fame liquor four or five days ; then being rinfed it is to be dyed in a warm bath, con- taining about twelve ounces, of kermes to each pound of wool. Lacca y or gumlac, a production of certain infefls, fomething in its nature like bees-wax, is brought from the Baft Indies, in form either of fticklac, N ON DYKING* f66 feed lac, or lump lac. It is ufed almoft folely for dyeing what is called red Morocco leather. Madder is chiefly ufed in dyeing linen and cotton {luffs red, and by admixture with other fubftances in dyeing them of other colours. A very beautiful and lively red is produced by adding ox's gall to the madder bath. If the ufual proportion of tartar in the preparation of the bath, which is from one fevepth to one fourth, is much increafed, a deep and durable cinnamon is produced. Archil is fold in the form of a pafte. It is made by powdering and fteeping in chamber-lie and lime, either the lichen roccella , or the lichen parellus. The former called herb, or Canary archil, the latter ground or Auvergne archil. It gives a beautiful though fading lilac colour to filks, and is ufed, mixed with other dyes, to deepen their fliades and give a bloom. Carthamus , a dye made of the bloffoms of a plant called carthamus tinftorius , cultivated in Spain, Egypt, and on the coaft of the Levant, is ufed for giving a poppy red to filk, and in dyeing orange red, cherry red, rofe, and flefh colour. When diffolved by an alkali, and precipitated by lemon juice, a powder is obtained, which, when mixed with finely pulverized talc, forms that beautiful pigment rouge. Brazil wood imparts all its colouring matter to water by boiling; and wool, previoufly alumed, ;; ON DYEING. 267 is dyed a good red by gently boiling in this deco&ion. Yellows. All the fub fiances employed for dyeing yellow colours are vegetable produ&ionSc The chief are weld, fuftic, arnotta, quercitron bark, and fumach. Weld is prepared from the rejeda luteola of bota- nifts. It was very much ufed formerly in dyeing a yellow, but is now daily giving way more and more to the ufe of quercitron bark. If arnotta be added to the weld bath, a golden or jonquil colour is produced. Fuftic is the wood of a tree called mortis tine - toria . According to the quantity employed it gives a yellow of different fliades, from a lemon to a reddifh yellow colour. Arnotta is a pafle procured from the feeds of an American plant called hixa orellana . It gives a reddifh yellow, and is chiefly employed as a ground colour for other dyes. Quercitron bark is got from a fpecies of oak called quercus nigra . Dr. Bancroft, who firft introduced it, has the foie right of importing and felling it* It contains ten times as much colouring matter as the fame quantity of weld, and will probably fooix entirely fuperfede the ufe of it. Sumach , which is the powdered root of a plant of that name, gives a durable yellow to cottons pre- vioufly prepared with the aluminous mordant. N 2 £68 ON DYEING, There are many other vegetables which may occa- fionally be had recourfe to for dyeing a yellow. The faw-wort, dyer’s broom, leaves of the fweet willow, and the bark of the Lombardy poplar, may all be ufed for this purpofe. The green outer rind of the walnut gives to wool a good fawn colour, and requires no mordant to fix it, though if a mor- dant be ufed it improves its luftre. Blues. The principal blue dyes are from in- digo, woad, logwood, and Pruffian blue. Indigo is prepared by a long and tedious pro- cefs from a plant caHed indigofera , cultivated both in America and the Eafl Indies. One part of indigo diifolved in fix or eight parts of ftrong fulphuric acid, and afterwards diluted with water, forms the dye called Saxon blue. To dye filks with what is called Englifh blue, the filk mull be firfl dyed a light blue, then dipped in hot water, and waflied in a flream, and laftly immerfed in the bath compofed of indigo diffolved in fulphuric acid with a fmall quantity of the folu- tion of tin. And there it mull be left till it has acquired the proper fhade. Woad is a kind of pafte prepared in this country by grinding and fermenting the leaves of the ifatis tinfioria , or, as it is called in Englifh, the woad plant. The blue colour which it affords is much inferior in luftre, but is more permanent than that from indigo. Thefe two dyes are mixed in forming ON DYEING. 26 9 the blue vat or bath in which all woollen goods are dyed blue. Logwood , called alfo Campechy or Jamaica wood, is boiled in water with a little alum, and a little verdigrife, when employed for dyeing blue ; but it is much more frequently ufed in dyeing blacks and grays, as will prefently appear. PruJJian blue is a chymical compound of iron and a peculiar acid, called Pru flic acid. Both the mode of obtaining and the mode of ufing this dye are intricate and complicated ; too much fo to prove interefting in their detail. The dye which it affords is very beautiful and very durable. Compound Colours. In dyeing, the com* pound colours are produced fometimes by mixing the Ample colours in the bath or dyeing liquor, and fometimes by dyeing the fluff firft in a bath of one Ample colour, then in that of another. Scarlet, green, purple, violet, and black are the compound colours that I fhall now proceed to notice. Scarlet is a compound of red and yellow. The moft common mode of dyeing a bright fcarlet is by means of the cochineal vat, which is thus prepared. In the Arft place, diffplve one part of fal ammo- niac in eight parts of nitric acid, at a temperature of 30° Fahrenheit’s. Then add, by very fmall portions, one part of tin, and afterwards dilute with a fourth of its weight of water. This is now a N 3 2 70 ON DYEING. nitro-Tnuriate of tin, or folution of tin in aquafortis and fpirit of fait. To make the dy v eing liquor, put eighteen ounces of this folution into a tin boiler, nearly filled with clear water; then add ten ounces of tartar, and fix of cochineal, and boil the mixture. The cloth to be dyed is now to be immerfed, and the boiling continued till it has received a good colour. By adding a little turmeric, which is a yellow dyeing drug, the fcarlet is rendered more lively. Doftor Bancroft propofes to fubfiitute quercitron bark for the tartar, and fays, that a farther improve- ment in the fcarlet dye is effeEled by ufing fulphuric acid inftead of the nitric acid, or aqua-fortis, in making the folution of tin. A good crirnfon is produced by boiling the cloth, dyed as above, in a folution of alum, or by boil- ing in alum and tartar find, and then dyeing with cochine d. Silk, that is to be dyed crirnfon, fhould not be thoroughly fcoured, its natural yellow hue being favourable to this dye. Articles firft dyed red with madder, then in a yellow dye of weld, or quercitron bark, have a cinnamon colour. When walnut. peel is ufed for the yellow, the refult is a chefnut, mufk, or fnuff colour; all of which, like fcarlet, are compounds of red and yellow. Thread and cotton take a cinnamon colour ON DYEING. £71 when firft dyed with verdigrife and weld, then dipped into a folution of' green vitriol, afterwards into a dcco&ion of galls, and laftly dyed in the madder bath. Green is a compound of blue and yellow. 'To dye woollens and cottons of this colour, it is moft advifeable to give the blue colour firft, and then the yellow. Woad is commonly ufed for the former, and weld or quercitron bark for the latter. But for the Saxon green dye, indigo is the blue, and fuftic the yellow, that is preferred. For very deep greens it is neceffary to ufe logwood and green vitriol, as in dyeing blacks, only in fmaller quan- tities. In giving a green dye to ft lk, the yellow bath is firft applied ; and to deepen the colour, or vary its hue, decoftion of logwood, fuftic, or arnotta, is added to the yellow bath, after the weld has been taken out. Violets , purples , and lilacs , are compounds of red and blue. In dyeing of thefe colours the blue ground is given firft; which, even for a dark purple, fhould not be deeper than a fky-blue. Logwood with galls gives feveral (hades of purple to wool that has been previously dyed blue. Any of the red and blue dyes may be ufed for thefe Colours; the feleflion of which, and the determi- ning their proportions for different tints and (Lades N 4 272 ON DYEING. requires a great degree of experience, and a great deal of nicety in the operator. Black cannot be confidered a colour, thofe bodies only appearing black which abforb all and refleft none of the prifmatic rays. With refpeft to the dyer’s art, however, it ftands upon the fame foot- ing with any of the colours which we have men- tioned. To dye a black is as proper an exprcffion as to dye a blue. By the firfl is meant to impregnate fubflances with fuch particles as fhall make them capable of abforbing all the prifmatic rays, and by the laft is meant to impregnate with fuch par- ticles as fhall enable the fubflance dyed to abforb all but the blue rays, which being confequently re- flected, produce on the organ of vilion the fenfation which we call a blue colour. To give cloth a good black, it fhould be prc- vioufiy dyed a deep blue, and cleanfed by full- ing. It fhould then be dipped into a decocfion of galls, and a bath oi logwood and green vitriol alternately, feveral times fucceffively, being ex- pofed for a little time to the air between each immerfion. To dye filk black it mull be firft cleaned by boiling with foap, beetling, and wafhing it well , it is then to be foaked for feveral hours in a warm decoftion of galls ; and laflly immerfed ON DYEING. %7S three or four times in the bath of logwood and green vitriol. Grays are only {hades of black, and are pro duced by the fame fubftances ufed in fmaller quantities. N 5 574 ESSAY XXIV. OF TANNING. The hides or fkins of almoil all animals are con- verted to fome ufeful purpofe. The hair, wool, or fur of fome is the part employed, in others it is the {kin itfelf. The preparation of the fkins is different accord- ing to their kinds, and according to their intended ufes. The ftrong hides of oxen are wholly prepared by the tanner, when intended for the foies of fhoes and boots ; but fuch as are intended for harnefs leather, and for coach leather, are afterwards fubrnitted to the currier’s art. The fkins of horfes, and of calves, are always curried, being ufed for the upper leathers of fhoes and boots ; and the fkins of fheep, deer, dogs, and fome other animals, are prepared for a variety of purpofes by the fellmonger and leather-dreffer. The converfion of hides and fkins into feather is always effefted by the procefs of tanning, which is the art that I now intend to take into confedera- tion. ' OF TANN I KG* In tanning, the objefk is, to convert the foft and porous hide into a hard compafl fubffance, not eafily . piltrefcible, and in a great degree impenetra- ble to water; in which Sate it is called leather. This objeft has always been chiefly effected by impregnating the fubffance ot the hide with oak bark or tan, which i$ done by {differing the hides to remain immerfed for a long time in an infufion of the bark in water, called by the tanners, -ooze.' Different plans have been propofed' and adopted in different tan-yards, for extracting the virtues of the bark, "and for impregnating the Rides with the fame. ' J The grand objefl to be attempted is to fave both bark, and time ; the latter ‘of which has been chief- ly attended to by the n ew tanners. Before noti- cing, however, the late improvements, it will be r ight to give a concife description of what is Termed the old mode of tanning, which has been adopted for many generations with fcafceiy any alterations, and is ftill moft generally followed in this country ♦ To prepare the {kins ior the tan pit, they are firft waffled, arid cleanfed, if poffible in running water ; #- tlie loofe cellular membrane is then cut away, which part of the procefs is called flefhing. After this, the hair is to be taken off, which is called depila.tion, and is effected by different means by different tan- ners. £76 OF TANNING. Some do it by laying the fkins in heaps, and leaving them together, till a putrefaftion com- mences, which loofens the hair, and makes it very eafy to be fcraped off. This plan, however, re- quiring great care, left the putrefa&ion fhould ad- vance too far, and injure the fkin, is pretty gene* rally laid afide as inconvenient. A fecond mode of effefting tbs depilation, is by immerfing the fkins for two or three days in lime water, and then fcraping off the hair, which the lime has loofened. This plan is almofl always adop- ted for calf fkins, but for the flronger hides it is lefs generally approved of, becaufe, it being necef- fary by wafhing and prefling to extract all the lime before the application of the tan, in thefe thick fkins it becomes a laborious and tedious procefs. A third mode of depilation is by immerfion in an acid liquor, namely, the fulphuric acid, or oil of vitriol, very much diluted, as one pint of acid to a hundred and twenty gallons of water. After two or three days immerfion the hair is loofened, and very eafily lcraped off. The laft improvement in this part of the bufinefs is to ufe the infufion or ooze, after it is become exhaufled of its tanning principle, inftead of water, to dilute the acid with. After depilation there is a procefs called raiftng % which is often but not conflantly had recourfe to, with a view of opening the pores, and rendering OF TANNING. 277 the hide more pervious to the tanning principle. This is done by fteeping the hides in an alkaline lie, and then fuffering them to remain ten or twelve hours in a vat of acid liquor, having twice as much acid in it, as that recommended for loofening the hair. The hides and fkins prepared in one or other of the above ways are now to be fubje&ed to the tan- ning, properly fo called. The ufual mode of doing this is to immerfe them in pits or vats containing the oak bark, coarfely powdered, and a proper quantity of water. It is neceflary to immerfe them firft in a weaker, then in a ftronger ooze, till at laft the fkins are laid in alternate layers with the bark, and the pits then filled with water. The hides require twelve, eighteen, and fometimes twenty-four months im- merfion, to be fully faturated with the tanning prin- ciple. During this procefs the hides require what is termed handling, to be repeated very frequently at firft, but not fo often as they are advanced to the ftronger oozes. This confifts in removing them from the liquor, expofing them for a fhort time to the air, and immerfing them again in the pits. The tan by this means gets more uniformly appli- ed to the furface of the hide, and any folds or wrin- kles that are made at one time are fmoothed out at another. £78 OF TANNING. But, befides this, I believe handling to have other effeQs, in confequence of fome chymical ac- tion of the air and light ; for it is a faft, known to experienced tanners, that handling is more ufeful in a funny day than in cloudy weather, in an expo- fed fituation than a fheltered one, and much more fo in warm than in cold weather. From certain fafts refpefting the depofition of tan from an infufion of bark when expofed to the air, and certain appearances when treated with a folution of glue in clofe and open veffels, I am inclined to believe, that the procefs ot handling is of much more importance than it is generally confidered to be, alid that hides would much fooner take the tan, if fome eafy means were contrived for expofing them much more frequently to the air and light ; in the fame way that many dyes are taken much more fpeedily and effectually by occafionally removing the fluff, and expofing it to the air, than if it be al- lowed to remain conftantly in the dyeing liquor. A good black cannot be given to cloth without fuch repeated expofures. Such is the ufual mode of tanning. Many im- provements have been propofed, fome of which we fhall now notice. Oak bark I have flated as the fubflance moft generally employed, but a variety of other barks contain the tanning principle ; as that of the afh, the willow, the poplar, the chefnut, &c. The barks of thefe trees may, and have been, OF ^TANNING. 279 very adyantageoufly employed In certain filia- tions.. The ufe of oak leaves has been propofed as a fubflitute for bark ; and, as they would require a great deal of ftore-room, it has been propofed to form an extract from them, to be ufed as required ; but I know not whether the plan has ever been adopted. Dr. Macbride, of Dublin, recommends the ufe of lime water inftead of plain water for making the ooze, it being well known that lime water will form a ftronger infufion than plain water from the fame quantity of bark. Whether it has been found to anfwer in tanning, I know not, but believe it to be very feldom if ever praftifed. Mr. Samuel Alhton, of Sheffield, obtained a pa- tent for a new mode of tanning, in which he pro- felfes to employ nothing but mineral fubftances. An Italian has propofed the following deviations from the eflabliffied mode of tanning. 1ft. To foak the green hides feparately in running water for a' length of time, fufficient to extraft all the lymph, which is known by putting a piece of the hide into water, and gradually heating it ; if no fcum rifes to the furface, it is a proof that no more lymph re- mains. 2dly. To immerfe them for one hour in water, heated to 167° Fahrenheit; ta fcrape off the hair as ufual, and then expofe to a ftream of water at 167° till the water contains no more animal jelly, which is known by evaporating a portion of it. 280 OF TANNING# Sdly. To take off the loofe membraneous parts, wafli in cold water, and then tan them in an ooze kept at 167° which has been filtered from the tan or bark. The warm ooze has been ufed by feveral tanners in this country, but is now lefs approved of than at fir ft. The mo ft important improvements in the art of tanning have been made by a Frenchman of the name of Seguin, and his plan is known to tanners of this country under the name of Defmond’s plan. As thefe improvements are grounded on the chy- mical qualities of the tan or bark, and on the chy- mical combination of the tanning principle and the hide, in the formation of leather, I fhall precede an account of his plan with a few obfervations upon thefe points. When a folution of green vitriol in water is add- ed to an infufion or decoction of oak bark, of galls, of afh bark, or any other of the tanning barks, it immediately ftrikes a black colour; and fuch fubftances have been confidered more or lefs aftrin- gent, as the vitriol has caufed a deeper or a fainter black. All fubftances poffeffmg this quality have been called aftringent ; all fuch fubftances have been confidered as poffeffmg the tanning quality ; and the property of tanning, it has been concluded, depends upon this aftringent principle ; and hence it has been haftily inferred, that, in proportion, OF TAN N INC. ^8 1 as the vitriol ftrikes a blacker colour does the aftringent fubftance pofiefs a ftronger tanning pro- perty. Later chymifts, dete&ing an acid in thefe aftrin- gent vegetables, which they have called the gallic acid, or acid of galls, have attributed to this acid the property of finking black with vitriol, and have alfo confidered it as the true tanning principle. Thefe opinions are now found to be erroneous. There are in the barks above fpecified, and in other vegetables, two diftinfl: principles ; the one link- ing a black with green vitriol, called gallic acid ; the other tanning or forming leather when combined with the fubftance of the hide, called properly tan- nin. Thefe two principles exift indifferent proportions in different fubftances ; and their prefence is eafily detefted feparately, by certain chymical tefts. The mode of judging of the tanning quality of any particular bark by the colour produced on add- ing green vitriol, is therefore very inaccurate. To dete6t the tannin or tanning principle in any fubftance, add a few drops of the folution of ani- mal glue (made by diffolving a little common glue in water over a moderate fire] to a wine glafs full of an intufion of the fubflance to be examined. If tannin is prefent, the liquor becomes turbid, and a whitifh fubftance tails to the bottom, which is a true powder of leather, being a compound of tannin and OF TANNING. glue, which glue is of the fame nature with the ikin or hide, that by union with tannin forms leather. The teff of gallic acid is green vitriol or cop- peras ; which, as .1 have before hated, {trikes a black, when added to any fubltance containing the gallic acid. Thefe two principles, it is true, very frequently, perhaps always, exifl together; but they exift in very different proportions in different vegetable pro- ductions, and are feparable from each other. The tannin is more foluble, and more eafily ex- traCted from the bark, than the gallic acid. Pour water upon powdered bark ; after an hour draw it off, and pour on frefh water; repeating this until the water is drawn off quite clear. This infuflon contains tannin as long as it is coloured, and will caufe a yellowifh or whitifh precipitate on addition of the folution of glue ; but the clear liquor no longer contains tannin, though it {till contains the gallic acid, as appears by its turning black when green copperas is added. After thefe obfervations, the directions of Mr. Defmond, for adopting Seguin’s mode oi tanning, will be more eafily comprehended. They are briefly as follows. Provide five digefters, having apertures at bot- tom ; place them near to each other, and elevate them upon {tillages. Fill them with ground tan, OF TANNING. £83 and pour water into the firft. After (landing a little time, draw r it off, and pour it on the tan in the fe- cond ; and fo on, till it has palled them all. When this liquor, which is called the tanning lixivium , is drawn off from the firft digefter, freih water mult be poured on, and pafs through all the digefters in the fame way. After this is repeated feveral times, the liquor no longer depofits a fediment on addition of the folution of glue, and therefore contains no more tannin. What paffes after this is to be kept feparately, and more water palled through, until it no longer gives a black colour with green copperas. This liquor is called the gallic lixivium , and is ufed iir- ftead of water in the procefs of depilation. The tan is now completely {pent or exhaulted, and mull be removed, that its place may be fupplied by freih. The tan in the other digefters will like- wife prefentiy be exhaufted, and require to be re- placed by freih in the fame manner. The tanning lixivium Ihould always be fo ftrong, , as to mark from fix to eight degrees on the hydro- meter for falts ; and when, therefore, what paffes from the laft digefter is of lefs ftrengtb, it muft be poured upon the frefh tan in the firft digefter. The hides and fkins being- wafiled and flelhed in o , the ufual way, are immerfed in a liquor formed of one part of fulphuric acid to a thou fan d of gallic lixivium ; and the hair is then to be fcraped off. 284 OF TANNING. Raifing is very feldom neceffary ; and the hides, being wafhed and drefted with the round knife, are fully prepared for tanning. Firft fteep the fkins or hides for fome hours in a weak lixivium of only one or two degrees, as that which runs from the fecond digefter, or fome that has been already ufed for tanning. Then put them into a flronger lixivium ; and after a few days renew the lixivium, which will now be found to be much weaker than at firft. Let it be renewed as often as it is found neceftary, until the hides are quite tan- ned, which may be known by cutting off a fmall piece of the edge. Now remove the leather, and dry it in a fihady place. The peculiarity in this mode of tanning is the ufing a ftrong infufion of the tan feparated from much of the gallic acid, inftead of immerfing the hides together with the bark in the tan pits. The advantage of it is the faving of time, hides being tanned in this way in fewer weeks than in months according to the old plan. Some tanners fay that it requires more bark, and that the leather is of an inferior quality. Others deny this, and affert the contrary. I believe the chief reafon, why this plan is fo little adopted in this country, is the uncertainty of the market. A tanner mull be daily receiving frefli hides, and fhould therefore be regularly difpofing of his leather ; otherwife [it lies long upon his hands, OF TANNING# 585 and he lafes in profit. Now in adopting this mode of tanning, which is fo fpeedy, there mud be fea- fons, when the tanner’s flock muft be immenfe; and of courfe the capital employed in fuch a trade muft be at one time very great, whilft at another he can employ but little. This inconvenience, added to the prejudices of old manufafturers againft all innovations, has re- tarded the introduftion of Defmond’s plan very confiderably. 28 a ESSAY XXV. OF CURRYING. The art of the currier confills in rendering the tanned fkins fupple and of uniform denfity ; in giving a proper grain, and in blacking fuch as are required to be of that colour. The leather, generally fubmitted to the currier’s art, is of the thinner fofter kind, as calf, feal, and dogfkins, horfe-hides, and the lighter cow-hides. The frronger hides are almolf folely employed for making the foies of boots and fhoes, and fuch require no preparation after tanning but what is effefted by the fhoemakers, after they are cut up into pieces fit for ufe. N Such, however, as are intended for coach and harnefs leather, are prepared by the currier; and hog-hides, ol which the feats of faddles are ufually made, likewife undergo part of the procefs of currying. Alter the face and ends of the {hanks have been cut off, if not previoufly done by the tanner, the currier commences his bufinefs by foaking the {kins in water, till they are completely wetted through. They are then taken out, and after draining are OF CURRYING. 287 placed upx>n fhort flatfided polls, called beams, to undergo what is termed the floaving. The workman handing behind the beam, (haves or cuts off the loofe cellular membrane from the flefh fide of the Ikin with a round-edged knife, having a double handle, and worked with both hands. The knife is firft carried lengthways, and then acrofs the (kin, from the back to the belly ; and by this procefs the different parts are brought to a more equal fubftance. The (kins, thus fhaved, are again immerfed in water, till they are well foaked, and are then brought out to be Jcoured . The fcouring is generally, and ought always to e, performed at twice ; the firft part of the pro- cefs being called water fcouring , and the latter flecking . For this purpofe the {kin is ftretched out upon a marble or ftone llab, and the water fcouring confiits in preffing along it with a thin blunt -edged ftone, fixed into a wooden handle, or with a lump of pumice ftone ; and in occafionally fcouring it with a hard brufh dipped in water. The (kin being again foaked in clean water, is taken out and fleeked ; which fleeking is done pre- cifely in the fame manner as the water fcouring, except that a blunt-edged iron inftrument, fixed into a wooden handle, and which is called a fleeker, is fubftituted for that of ftone. 3 588 OF CURRYING. The objefl: of the fcouring is to extraft all the lime, and other filth, that the leather had acquired in tanning; and the ufe of the fleeter, that is em- ployed laft, is to force out all the water, extend the fkin, and obliterate the natural grain. The more the fkin is extended, the finer grain will it after- wards affume. The next part of the procefs is to impregnate the leather with oil, which renders it fupple, and in a great meafure impervious to water. The fkins for this purpofe fhould only be half dried; and therefore in general, when fcoured, they are laid in heaps till wanted. But fometimes, for the fake of difpatch, they are hung up feparately in the fheds to undergo this partial drying ; and this is called by the workmen Jamming . To impregnate them with oil, or as the work- men term it, Jluff them , they are laid out upon tables, and firft the grain fide of the leather is rub- bed over with a mixture of cod oil, and an oil ob- tained from the leather dreffers, called fod oil. Then the flefh fide is rubbed over with a larger quantity of a mixture of fod oil and tallow, with only fo much cod oil as will render it of a proper confidence to be eafily fpread upon the leather. When the fkins are thus fluffed, they are again hung up feparately in airy fheds to dry; but before they become quite dry, they are taken down and Jet ; i. e. they are flretched out upon a table, and OF CURRYING. 589 the neck and other coarfe parts are prefTed with a flone, fimilar to that ufed in fcouring, with a view of extending them, taking out all wrinkles, and obliterating what may remain of the natural grain. They are then hung up again to be thoroughly dried, either in the flieds, or in ftoves, according to the weather. If flied-dried they require to be expofed laft of all to the funfhine. The procefs of currying, as far as we have now defcribed it, is termed by the workmen the putting out . It now remains to render the leather more fup- pie and pliable, to give it a grain, and to blacken it, if required. This part of the bufinefs is called the making up. The dried fkin is laid uport a large board with the grain fide upwards, and being doubled is rol- led with confiderable preffure upon the flefli fide firft, and afterwards upon the grain, with a fluted board, fattened to the operator’s hand by a ftrop. This rolling is done in the direftion from the hinder lhank to the cheek each way. To take off the greafe, that remains on the fur- face of the. leather, . the flefli fide is gone over with a fharp fleeker, and the grain rubbed with tow and the finer fhavings called whitenings. To complete this objeft, the fiefh fide is flightly fliaved v .th a fine-edged knife, which is called the whitenings and the grain is very highly fleeked, O OF CURRYING* a $0 . o give a grain to the leather, it is now rolled upo the flefh fide with a much finer fluted board than before, and with greater exa&nefs. Tne blacking, which is the only part of the bufinefs that remains to be defcribed, is perform- ed very differently on the different fides. Leather, that is to be blackened on the flefh fide, which is the cafe with molt of the finer leather for fhoes and boots, is blackened with lamp-black; and what is blackened on the grain fide, receives that colour from the application of copperas or green vitriol. For the firfl kind a mixture of lamp-black, cod oil and allow, with a fmall quantity of the water in which the leather was foaked previoufly to the {having, is rubbed into the flefh fide with a round brufh, and it is then brufhed over with ftrong fize and taUow. When this has dried, it is fleeked with a round fmooth-edged glafs flecker, and is laftly wafhed over with a weak fize, to fix the colour. The leather that is to be blackened on the grain fide, after being fhaved and fcoured as ufual, is brufhed over with chamberlie, and then with a lolution of green copperas. To prevent its {hiking too deep, it is then wafhed with water, and fleeked out. It is now to be fluffed as the other leather, but with a lefs proportion of tallow, and more fod oil. OF CURRYING. % 9 1 This fhoultl be done as foon as it conveniently can, left the copperas fhould injure the leather. When it has imbibed the oil, it is not expofed to the fun, but taken down, lloned quite fmooth, and again wafhed with the folution of copperas, till quite black. If any artificial grain is wanted, it is now im- printed with a piece of the dried fkin of the dog- fiih. If the natural grain is wifhed for, the (kin is rolled with a very fine fluted board upon the flefh fide in two or three directions, and laftly upon the grain with one ftill finer. The leather is now hung up to dry, either in the fun, or by the ftoves, and when dried is whiten- ed, but not with the fame care that the other kind requires. After whitening, it is again rolled with the fine fluted board, and the procefs is finifhed by rubbing it over with a fmall quantity of cod oil and tallow. In blacking the leather in this way, the copperas ads the fame, as when it is added to an infufion o£ bark or tan, which is immediately turned black by it. THE EN D* Printed b/BysandLAw, St, John’ S^uaie, Clerkenweli. Juft PubliJhedy IN THREE VOLUMES OCTAVO, Price 24s. in Boards, A HISTORY OF THE PROGRESS AND PRESENT STATE O F ANIMAL CHYMISTR.Y. B Y k ' W. B. JOHNSON, M. B. PRINTED FOR J. JOHNSON, IN ST, PAUL’S CHU.R.CK- YARD: F o O o ■ o o o * * o 4 o * O 5/^u t£L GETTY CENTER LIBRARY